chore(package): update rollup to version 1.15.3

Closes #26

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "microstates": "^0.13.0",
     "react": "^16.8.0",
     "react-dom": "^16.8.0",
-    "rollup": "1.2.0",
+    "rollup": "1.15.3",
     "rollup-plugin-babel": "^4.0.3"
   },
   "peerDependencies": {