Get TC to run 'npm run lint'

Met with owlish who answered a lot of my initial questions for this first milestone

.taskcluster.yml

@@ -3,13 +3,14 @@
 #  - https://github.com/taskcluster/taskcluster-github/blob/master/docs/taskcluster-yml-v1.md
 version: 1
 policy:
-  pullRequests: public
+  pullRequests: public # Run these tasks for qualifying GH events from any one in the repo
 tasks:
   # When a PR is opened, reopened or synchronized, perform this task
   - $if: 'tasks_for == "github-pull-request" && event["action"] in ["opened", "reopened", "synchronize"]'
     then:
-      # QUESTION - how does taskId vary? Seems like passing a static string each time.
-      taskId: {$eval: as_slugid("pr_task")}
+      # TC creates a task group with tasks in it; each task has an ID. TC will provide a link
+      # built with these IDs in GH's GUI every time a task is created, even if it fails.
+      taskId: {$eval: as_slugid("pr_task")} # Returns a hash of a string
       created: {$fromNow: ''}
       # If the task is not completed by its deadline, it will be resolved as `exception`
       # with reason "deadline-exceeded"
@@ -18,35 +19,29 @@ tasks:
       # (could be 1 CPU, a fraction of a CPU, multiple CPUs...)that will execute the
       # task. e.g. 'aws-provisioner-v1' is the AWS Provisioner, which runs its tasks
       # on Amazon EC2 instances using Docker.
-      # QUESTION - is this the right provisioner? In mythmon's v0, he had something like:
-      # '{{ taskcluster.docker.provisionerId }}'
       provisionerId: aws-provisioner-v1
       # A parameter specific to the AWS Provisioner which identifies the pool of EC2
       # resources within which the task should be executed. Pools may use different
       # EC2 instance types, AMIs (Amazon Machine Images), etc.
-      # QUESTION - is this the right worker? In mythmon's v0, he had something like:
-      # '{{ taskcluster.docker.workerType }}'
-      workerType: github-worker
+      workerType: github-worker # TC's generic worker for any github projects; can do Try server pushes
       # A scope is a permission to perform a particular action. A task has a set of
       # scopes that determine what the task can do. These scopes are validated by the worker.
-      scopes:
-        - secrets:get:project/taskcluster/testing/taskcluster-github # QUESTION - What scopes do I need?
       payload: # The format of a task's payload property is specific to the worker that will execute it
         maxRunTime: 600 # 10 minutes
          # QUESTION: Is this the right image? Where can I find all supported images? Do all images have
          # Firefox installed to push to Try? I want to run TALOS and mochitests in addition to unit tests
          # from my repo
         image: "node:8" # The Docker image to pull
-        env: # QUESTION: What is this?
-          DEBUG: "* -mocha* -nock* -express* -body-parser* -eslint*" # QUESTION: What is this? What does *, -mocha* etc. do?
-        features: # QUESTION: What is this?
-          taskclusterProxy: true # QUESTION: What does this mean?
+        env: # Environment variables to declare in the shell
+          DEBUG: "* -eslint*" # Say you have debug statements in library code; a DEBUG variable with a
+          # value of * will log all levels of debug statements
         command: # The command to run within that Docker image
           - "/bin/bash"
           - "-lc" # '--login' (executes user's profile commands), '-c' (executes commands from a string)
-          - >- # QUESTION: Will multi-line commands like this work in v1? Can I omit -c above?
+          - >-
             git clone ${event.pull_request.head.repo.git_url} repo &&
-            cd repo && git checkout ${event.pull_request.head.sha} &&
+            cd repo &&
+            git checkout ${event.pull_request.head.sha} &&
             npm install &&
             npm run lint
       # TODO bdanforth: Replace `npm run lint` above with `npm test`
@@ -55,37 +50,37 @@ tasks:
         description: "All tests"
         owner: ${event.pull_request.user.login}@users.noreply.github.com
         source: ${event.repository.url}
-  # When a commit is pushed to the repo, perform this task
+  # When a commit is pushed to master, perform this task
+  # If a branch is merged without being updated first, the tests could pass on the branch
+  # but not when things are merged into master.
   # QUESTION: Does this cover additional commits to an existing open PR?
   - $if: 'tasks_for == "github-push"'
     then:
-      taskId: {$eval: as_slugid("push_task")}
-      created: {$fromNow: ''}
-      deadline: {$fromNow: '1 hour'}
-      provisionerId: aws-provisioner-v1
-      workerType: github-worker
-      scopes:
-        - secrets:get:project/taskcluster/testing/taskcluster-github
-      payload:
-        maxRunTime: 600
-        image: "node:8"
-        env:
-          DEBUG: "* -mocha* -nock* -express* -body-parser* -eslint*"
-          NO_TEST_SKIP: "true"
-        features:
-          taskclusterProxy: true
-        command:
-          - "/bin/bash"
-          - "-lc"
-          - >-
-            git clone ${event.repository.url} repo &&
-            cd repo &&
-            git checkout ${event.after} &&
-            npm install &&
-            npm run lint
-      # TODO bdanforth: Replace `npm run lint` above with `npm test`
-      metadata:
-        name: "Taskcluster GitHub Tests"
-        description: "All tests"
-        owner: ${event.pusher.name}@users.noreply.github.com
-        source: ${event.repository.url}
+      $if: 'event.ref == "refs/heads/master"'
+      then:
+        taskId: {$eval: as_slugid("push_task")}
+        created: {$fromNow: ''}
+        deadline: {$fromNow: '1 hour'}
+        provisionerId: aws-provisioner-v1
+        workerType: github-worker
+        payload:
+          maxRunTime: 600
+          image: "node:8"
+          env:
+            DEBUG: "* -eslint*"
+            NO_TEST_SKIP: "true"
+          command:
+            - "/bin/bash"
+            - "-lc"
+            - >-
+              git clone ${event.repository.url} repo &&
+              cd repo &&
+              git checkout ${event.after} &&
+              npm install &&
+              npm run lint
+        # TODO bdanforth: Replace `npm run lint` above with `npm test`
+        metadata:
+          name: "Firefox Experiments GitHub Tests"
+          description: "All tests"
+          owner: ${event.pusher.name}@users.noreply.github.com
+          source: ${event.repository.url}