chore(package): update rollup to version 2.1.0

Closes #197

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "mocha-phantomjs": "^4.1.0",
     "nyc": "^15.0.0",
     "regenerator-runtime": "^0.13.0",
-    "rollup": "^1.21.4",
+    "rollup": "^2.1.0",
     "rollup-plugin-babel": "^4.0.0-beta.0",
     "rollup-plugin-replace": "^2.0.0",
     "rollup-plugin-uglify": "^6.0.0",