Update dependency grunt-contrib-clean to v2

Author: renovate[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "eslint-plugin-standard": "^5.0.0",
     "grunt": "^1.0.4",
     "grunt-cli": "1.5.0",
-    "grunt-contrib-clean": "1.1.0",
+    "grunt-contrib-clean": "2.0.1",
     "grunt-contrib-compress": "^2.0.0",
     "grunt-contrib-concat": "2.1.0",
     "grunt-contrib-copy": "1.0.0",