chore(CI): adjust build matrix

.travis.yml

@@ -1,24 +1,27 @@
 language: node_js
-node_js: "8"
+node_js:
+  - "8"
+  - "6"
+  - "4"
 jobs:
   include:
     - stage: test
       name: 'Linting'
+      node_js: "8"
       script: npm run lint
     - name: 'Unit Test'
+      node_js: "8"
       script: npm run unit && npm run coveralls
     - name: 'E2E Test'
       script: npm run e2e
-      node_js:
-        - "8"
-        - "6"
-        - "4"
 
     - stage: build
+      node_js: "8"
       script: npm run build
 
     - stage: release
       if: branch = master
+      node_js: "8"
       script: skip
       deploy:
         provider: script

package.json

@@ -17,9 +17,7 @@
     "demo:browser": "echo open http://localhost:8080/demo/browser && http-server -c-1",
     "demo:nodejs": "node ./demo/nodejs/index.js",
     "demo:express": "cd ./demo/express/ && npm start",
-    "preversion": "npm test",
-    "version": "npm run build && git add -A dist",
-    "postversion": "git push --tags"
+    "version": "npm run build && git add -A dist"
   },
   "repository": {
     "type": "git",