import Promise to src/rollup.js – fixes #254

src/rollup.js

@@ -1,3 +1,4 @@
+import Promise from 'es6-promise/lib/es6-promise/promise.js';
 import { basename } from './utils/path.js';
 import { writeFile } from './utils/fs.js';
 import { keys } from './utils/object.js';