Update rollup to the latest version 🚀 (#259)

Author: greenkeeper[bot]

package.json

@@ -75,7 +75,7 @@
     "null-loader": "^0.1.1",
     "pre-commit": "^1.2.2",
     "rimraf": "^2.6.2",
-    "rollup": "^0.51.5",
+    "rollup": "^0.52.0",
     "rollup-plugin-buble": "^0.18.0",
     "rollup-plugin-commonjs": "^8.2.1",
     "rollup-plugin-node-resolve": "^3.0.0",