chore(package): update rollup to version 2.1.0

Closes #24

Author: greenkeeper[bot]

package.json

@@ -68,7 +68,7 @@
     "nyc": "^14.1.1",
     "postcss": "^7.0.14",
     "postcss-inline-svg": "^4.0.0",
-    "rollup": "^1.20.0",
+    "rollup": "^2.1.0",
     "rollup-plugin-babel": "4.3.3",
     "rollup-plugin-commonjs": "^10.0.0",
     "rollup-plugin-json": "^4.0.0",