chore(package): update rollup to version 2.3.4

Closes #120

Author: greenkeeper[bot]

package.json

@@ -80,7 +80,7 @@
     "husky": "^4.2.3",
     "nyc": "^15.0.0",
     "prettier": "^1.19.1",
-    "rollup": "^1.31.1",
+    "rollup": "^2.3.4",
     "rollup-plugin-babel": "^4.3.3",
     "rollup-plugin-commonjs": "^10.1.0",
     "rollup-plugin-flow-entry": "^0.3.3",