chore(ci): simplify .travis.yml

Author: nikku

.travis.yml

@@ -1,20 +1,6 @@
 language: node_js
 node_js:
-  - "4"
   - "8"
-  - "9"
 
-before_install:
-  - "export BROWSERS=Firefox"
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
-
-after_success:
-  - yarn cover-publish
-addons:
-  code_climate:
-    repo_token:
-      # # get your token from https://codeclimate.com/github/benjamine/jsondiffpatch
-      # gem install travis
-      # travis encrypt <projecttoken>
-      secure: "IZabDj3HrrCNOfhK0v+Q/am9AE5zYzF13IYB64q8wSUHcSxxhdrxSyLvjIiOfLe9W+h+MAW1+OuQkldUs/yd/fJjy44GE4ugUKY+9RP3TBm7hQRF4KEwIx2BMK4HVNazOkWz8nsnq4cfPy9pFEumcKb/O7TL2gK6RS6dIfNsKw0="
+script:
+  - "npm run all"