chore(ci)!: Update tested Node versions

Also, only deploy to npm when tests pass on all Node versions.

BREAKING CHANGE: Dropping Node 6 from CI.

.travis.yml

@@ -1,13 +1,23 @@
 language: node_js
 node_js:
-  - '6'
-  - '8'
+  - '12'
   - '10'
+  - '8'
 after_success: npm run coveralls
-deploy:
-  provider: npm
-  email: nwoltman@outlook.com
-  on:
-    tags: true
-  api_key:
-    secure: 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
+stages:
+  - test
+  - name: npm release
+    if: tag IS present
+jobs:
+  include:
+    - stage: npm release
+      install: skip
+      script: skip
+      after_success: true # skip step with success exit code
+      deploy:
+        provider: npm
+        email: nwoltman@outlook.com
+        on:
+          tags: true
+        api_key:
+          secure: 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