Speed up CI (#1076)

* Stop testing Node.js v5

* Only upgrade npm when Travis runs Node.js older than v6

* Cache npm directories in Travis builds

* Stop retrying failed runs in Appveyor

Hopefully it's become more reliable since a73374d.

* Remove unnecessary clone_depth option from Appveyor

Per https://www.appveyor.com/docs/how-to/repository-shallow-clone/#downloading-repository-via-github-or-bitbucket-api

* Remove unnecessary version property from Appveyor

We're not building so the version isn't necessary.

* Cache npm directories in Appveyor builds

* Prune after npm install

Ensure top-level dependencies are indeed no longer available when
removed from the package.json.

* Ensure npm@3 for pre-v6 Node.js versions

Soon npm@latest will be npm@4. Let's stick to v3 for now.

.travis.yml

@@ -1,11 +1,16 @@
 language: node_js
 node_js:
   - '6'
-  - '5'
   - '4'
   - '0.12'
   - '0.10'
+cache:
+  directories:
+    - $HOME/.npm
+    - node_modules
 before_install:
-  - 'npm install -g npm@latest'
+  - 'node -e "process.exit(Number(process.version.match(/^v(\d+)/)[1])>=6?0:1)" || npm install -g npm@3.x-latest'
+before_script:
+  - npm prune
 after_success:
   - '[ -z "$COVERALLS_REPO_TOKEN" ] && tap --coverage-report=text-lcov | ./node_modules/.bin/coveralls'

appveyor.yml

@@ -1,23 +1,24 @@
 environment:
   matrix:
     - nodejs_version: '6'
-    - nodejs_version: '5'
     - nodejs_version: '4'
     - nodejs_version: '0.12'
 install:
   - ps: Install-Product node $env:nodejs_version
   - set CI=true
   - set AVA_APPVEYOR=true
-  - npm install -g npm@latest || (timeout 30 && npm install -g npm@latest)
+  - npm install -g npm@3.x-latest
   - set PATH=%APPDATA%\npm;%PATH%
-  - npm install || (timeout 30 && npm install)
+  - npm install
+  - npm prune
 matrix:
   fast_finish: true
 build: off
-version: '{build}'
 shallow_clone: true
-clone_depth: 1
+cache:
+  - node_modules
+  - '%APPDATA%\npm-cache'
 test_script:
   - node --version
   - npm --version
-  - npm run test-win || (timeout 30 && npm run test-win)
+  - npm run test-win