Fixed typo

Author: killme2008

lib/cloud.js

@@ -195,7 +195,7 @@
    AV.Cloud.afterDelete = function(name, func){};
 
    /**
-    * Registers a on-login function.
+    * Registers an on-login function.
     * <br/><strong>Available in Cloud Code only</strong>.
     * If you want to use onLogin for an user in the AV JavaScript SDK, you should pass the function:
     * <code><pre>