Run tests on node 10. Drop support for node 4.0

Author: IvanGoncharov

.babelrc

@@ -2,7 +2,7 @@
   "presets": [["env", {
     "modules": false,
     "targets": {
-      "node": 4,
+      "node": 6,
       "browsers": [
         "ie 9",
         "ios 9",

.travis.yml

@@ -1,11 +1,11 @@
 language: node_js
 
-# https://github.com/nodejs/LTS
+# https://github.com/nodejs/Release
 node_js:
+  - '10'
   - '9'
   - '8'
   - '6'
-  - '4'
 
 git:
   depth: 5

package.json

@@ -17,6 +17,9 @@
   "options": {
     "mocha": "--check-leaks --full-trace --timeout 15000 src/**/__tests__/**/*-test.js"
   },
+  "engines": {
+    "node": "6.x || 8.x || >= 9.x"
+  },
   "scripts": {
     "watch": "babel-node ./resources/watch.js",
     "test": "npm run lint && npm run check && npm run testonly",