feat: drop Node v4

BREAKING CHANGE: Dropped Node v4.

Author: gajus

.babelrc

@@ -4,6 +4,10 @@
     "add-module-exports"
   ],
   "presets": [
-    "es2015"
+    ["env", {
+      "targets": {
+        "node": "current"
+      }
+    }]
   ]
 }

.travis.yml

@@ -3,7 +3,6 @@ node_js:
   - 7
   - 6
   - 5
-  - 4
 before_install:
   - npm config set depth 0
   - npm install --global npm@latest

package.json

@@ -13,7 +13,7 @@
     "babel-cli": "^6.18.0",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-plugin-transform-flow-strip-types": "^6.18.0",
-    "babel-preset-es2015": "^6.5.0",
+    "babel-preset-env": "^1.2.2",
     "babel-register": "^6.18.0",
     "chai": "^3.5.0",
     "eslint": "^3.10.2",
@@ -23,6 +23,9 @@
     "mocha": "^2.5.3",
     "semantic-release": "^6.3.2"
   },
+  "engines": {
+    "node": ">=5"
+  },
   "keywords": [
     "eslint",
     "plugin",