build: Update grunt to fix security issue

npm:
* grunt: 1.0.3 → 1.0.4
  * https://npmjs.com/advisories/788
  * https://npmjs.com/advisories/813

Change-Id: I26b83a2409192e358da4a43768fd7fc246751935

package.json

@@ -5,7 +5,7 @@
 	},
 	"devDependencies": {
 		"eslint-config-wikimedia": "0.9.0",
-		"grunt": "1.0.3",
+		"grunt": "1.0.4",
 		"grunt-banana-checker": "0.6.0",
 		"grunt-eslint": "21.0.0",
 		"grunt-jsonlint": "1.1.0",