fix: support Node.js v4 (#101)

Author: 0x6b

.babelrc

@@ -4,8 +4,9 @@
       "env",
       {
         "targets": {
-          "node": 6
-        }
+          "node": 4
+        },
+        "exclude": ["babel-plugin-transform-regenerator"]
       }
     ]
   ]

.travis.yml

@@ -1,6 +1,7 @@
 sudo: false
 language: node_js
 node_js:
+  - 4
   - 6
   - 7
 notification:

package.json

@@ -3,7 +3,7 @@
   "version": "4.1.2",
   "description": "A textlint rule to check if all links are alive",
   "engines": {
-    "node": ">=6"
+    "node": ">=4"
   },
   "main": "lib/no-dead-link.js",
   "scripts": {