chore(package): update rollup to version 0.50.0

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "underscore": "1.8.3",
     "jsdoc-to-markdown": "^3.0.0",
     "markdown-doctest": "^0.9.1",
-    "rollup": "^0.49.3",
+    "rollup": "^0.50.0",
     "nyc": "^11.2.1"
   },
   "contributors": [