chore(deps): update dependency rollup to v1.21.0

Author: renovate-bot

package.json

@@ -79,7 +79,7 @@
     "react": "16.9.0",
     "react-dom": "16.9.0",
     "rimraf": "3.0.0",
-    "rollup": "1.20.3",
+    "rollup": "1.21.0",
     "rollup-plugin-babel": "4.3.3",
     "rollup-plugin-commonjs": "10.1.0",
     "rollup-plugin-node-resolve": "5.2.0",