Wrap file into IIFE

This pull request offers to wrap file source into an IIFE to avoid polluting global namespace with find/findIndex/contains functions.
This might be considered to be done in a GruntTask too.

Author: killzoner

src/angularjs-dropdown-multiselect.js

@@ -1,3 +1,5 @@
+(function (angular) {
+
 'use strict';
 
 var directiveModule = angular.module('angularjs-dropdown-multiselect', []);
@@ -562,3 +564,5 @@ function findIndex(collection, properties) {
 
 	return index;
 }
+
+})(angular);