Add empty ignore array to bower.json

Bower throws a in “invalid-meta” warning saying “jquery-ui is missing
"ignore" entry in bower.json” when this array is not available.

Cf. <#37>

Addresses #37

Author: ltrebing

bower.json

@@ -4,6 +4,8 @@
   "main": [
     "jquery-ui.js"
   ],
+  "ignore": [
+  ],
   "dependencies": {
     "jquery": ">=1.6"
   }