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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