chore(package): update rollup-plugin-uglify to version 6.0.2

Closes #29

Author: greenkeeper[bot]

package.json

@@ -20,7 +20,7 @@
     "rollup-plugin-commonjs": "^7.0.0",
     "rollup-plugin-node-resolve": "^2.0.0",
     "rollup-plugin-string": "^2.0.2",
-    "rollup-plugin-uglify": "^1.0.1",
+    "rollup-plugin-uglify": "^6.0.2",
     "snazzy": "^6.0.0",
     "watch": "^1.0.1",
     "whatwg-fetch": "^2.0.0"