chore(package): update rollup to version 0.61.2

Closes #12

Author: greenkeeper[bot]

package.json

@@ -56,7 +56,7 @@
     "json-stable-stringify": "^1.0.1",
     "mocha": "^5.0.4",
     "parse-json": "^4.0.0",
-    "rollup": "^0.60.0",
+    "rollup": "^0.61.2",
     "rollup-plugin-babel": "^3.0.3",
     "semantic-release": "^15.0.0",
     "sinon": "^6.0.0",