ci: test Node.js 6, 8, 10 and 11 (#69)

Author: DanielRuf

.travis.yml

@@ -8,13 +8,16 @@ matrix:
   fast_finish: true
   include:
     - os: linux
-      node_js: '6'
+      node_js: 'node'
+      env: WEBPACK_VERSION="2.2.0" JOB_PART=test
+    - os: linux
+      node_js: '10'
       env: WEBPACK_VERSION="2.2.0" JOB_PART=test
     - os: linux
-      node_js: '4.3'
+      node_js: '8'
       env: WEBPACK_VERSION="2.2.0" JOB_PART=test
     - os: linux
-      node_js: '7'
+      node_js: '6'
       env: WEBPACK_VERSION="2.2.0" JOB_PART=test
     # - os: linux
     #   node_js: '7'