chore(package): update rollup to version 0.67.4 (#9)

Author: greenkeeper[bot]

package.json

@@ -86,7 +86,7 @@
     "react-router-dom": "^4.3.1",
     "react-scripts": "1.1.4",
     "react-test-renderer": "^16.6.0",
-    "rollup": "^0.66.6",
+    "rollup": "^0.67.4",
     "rollup-plugin-babel": "^4.0.3",
     "rollup-plugin-commonjs": "^9.1.3",
     "rollup-plugin-node-resolve": "^3.3.0",