build: Updating npm dependencies for security issues

* Updated stylelint-config-wikimedia to 0.6.0, addressing:
  * https://npmjs.com/advisories/786

Committed package-lock.json (T179229) too.

Change-Id: I4aee6ef5480f4e26b264e757e0288e8e071fd028

.gitignore

@@ -5,3 +5,4 @@
 *.kate-swp
 .*.swp
 composer.lock
+.eslintcache

package.json

@@ -6,7 +6,7 @@
 		"grunt-banana-checker": "0.6.0",
 		"grunt-eslint": "21.0.0",
 		"grunt-stylelint": "0.10.1",
-		"stylelint-config-wikimedia": "0.5.0"
+		"stylelint-config-wikimedia": "0.6.0"
 	},
 	"scripts": {
 		"test": "grunt test"