tests - add fetch polyfill

package.json

@@ -117,6 +117,7 @@
     "gulp-util": "^3.0.7",
     "gulp-watch": "^4.3.5",
     "gulp-zip": "^3.2.0",
+    "isomorphic-fetch": "^2.2.1",
     "jsdom": "^8.1.0",
     "jsdom-global": "^1.7.0",
     "jshint-stylish": "~0.1.5",

test/unit/config-manager-test.js

@@ -1,8 +1,10 @@
+// polyfill fetch
+global.fetch = global.fetch || require('isomorphic-fetch')
 const assert = require('assert')
 const extend = require('xtend')
 const rp = require('request-promise')
 const nock = require('nock')
-var configManagerGen = require('../lib/mock-config-manager')
+const configManagerGen = require('../lib/mock-config-manager')
 const STORAGE_KEY = 'metamask-persistance-key'
 
 describe('config-manager', function() {