fix(test): add es6-shim to test env

Author: robwormald

karma.conf.js

@@ -16,6 +16,7 @@ module.exports = function(config) {
 
     // list of files / patterns to load in the browser
     files: [
+      'node_modules/es6-shim/es6-shim.js',
       'node_modules/systemjs/dist/system.js',
       'spec/support/karma-system.js',
       'node_modules/reflect-metadata/Reflect.js',