Breaking: require node >= 6 & eslint >= 5 (fixes #70)

Author: aladdin-add

.travis.yml

@@ -1,6 +1,7 @@
 language: node_js
 node_js:
-  - '4'
   - '6'
-  - '7'
   - '8'
+  - '9'
+  - '10'
+  - '11'

package.json

@@ -44,9 +44,9 @@
     "mocha": "^3.4.2"
   },
   "peerDependencies": {
-    "eslint": ">=4.1.0"
+    "eslint": ">=5.0.0"
   },
   "engines": {
-    "node": ">=4.0.0"
+    "node": "^6.14.0 || ^8.10.0 || >=9.10.0"
   }
 }