Fix typing mistake: "fasle" instead of "false"

Author: Thierry Régagnon

select2.js

@@ -396,7 +396,7 @@
      */
     function checkFormatter(formatter, formatterName) {
         if ($.isFunction(formatter)) return true;
-        if (!formatter) return fasle;
+        if (!formatter) return false;
         throw new Error("formatterName must be a function or a falsy value");
     }