Build Tools: Add an npm script shortcut to run grunt.

Rather than needing to install grunt globally, this allows running grunt from node_modules, instead.

npm run grunt ... is effectively the equivalent of running grunt ....

Props andrew.taylor, pento.
Merges [43836] to trunk.
See #45214.


git-svn-id: https://develop.svn.wordpress.org/trunk@44176 602fd350-edb4-49c9-b593-d223f7449a82

package.json

@@ -106,5 +106,8 @@
 		"twemoji": "11.0.0",
 		"underscore": "1.8.3",
 		"whatwg-fetch": "^3.0.0"
+	},
+	"scripts":{
+		"grunt": "grunt"
 	}
 }