chore: allow node v4

Author: gajus

package.json

@@ -36,7 +36,7 @@
     "postcss-scss": "^0.4.0"
   },
   "engines": {
-    "node": ">5.0.0"
+    "node": ">4.0.0"
   },
   "keywords": [
     "babel-plugin",