[package] revert eslint, let's comply with new ruls after release

Author: ar2rsawseen

package.json

@@ -20,7 +20,7 @@
     "grunt-contrib-copy": "1.0.0",
     "grunt-contrib-cssmin": "3.0.0",
     "grunt-contrib-uglify": "4.0.1",
-    "grunt-eslint": "^22.0.0",
+    "grunt-eslint": "^21.0.0",
     "grunt-mocha-nyc": "^1.0.3",
     "grunt-mocha-test": "0.13.3",
     "mocha": "^6.2.0",