use promise-polyfill so it still works in older versions of node

Author: joshwnj

index.js

@@ -1,3 +1,6 @@
+// Some css-modules-loader-code dependencies use Promise so we'll provide it for older node versions
+if (!global.Promise) { global.Promise = require('promise-polyfill') }
+
 var fs = require('fs');
 var path = require('path');
 var through = require('through');
@@ -6,7 +9,6 @@ var FileSystemLoader = require('css-modules-loader-core/lib/file-system-loader')
 var assign = require('object-assign');
 var stringHash = require('string-hash');
 
-
 /*
   Custom `generateScopedName` function for `postcss-modules-scope`.
   Short names consisting of source hash and line number.

package.json

@@ -5,6 +5,7 @@
   "main": "index.js",
   "dependencies": {
     "css-modules-loader-core": "^1.0.0-beta4",
+    "promise-polyfill": "^2.1.0",
     "object-assign": "^3.0.0",
     "string-hash": "^1.1.0",
     "through": "^2.3.7"