🐢 feat: Version Node engine in package.json

- Enforces Node version due to use of `let`, `const`, and `Promise`
  according to http://node.green/

Author: dflynn15

package.json

@@ -1,6 +1,6 @@
 {
   "name": "scss-splinter",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "description": "",
   "main": "index.js",
   "scripts": {
@@ -18,5 +18,8 @@
     "url": "[email protected]:sparkbox/splinter.git",
     "type": "git"
   },
-  "author": "Adam Simpson <[email protected]>"
+  "author": "Adam Simpson <[email protected]>",
+  "engine": {
+    "node": ">=4.3.2"
+  }
 }