docs($rootScope): fix $on listener signature doc

Added args in $on() listener syntax declaration

Author: unirgy

src/ng/rootScope.js

@@ -614,8 +614,8 @@ function $RootScopeProvider(){
        * @param {function(event)} listener Function to call when the event is emitted.
        * @returns {function()} Returns a deregistration function for this listener.
        *
-       * The event listener function format is: `function(event)`. The `event` object passed into the
-       * listener has the following attributes
+       * The event listener function format is: `function(event, args...)`. The `event` object
+       * passed into the listener has the following attributes:
        *
        *   - `targetScope` - {Scope}: the scope on which the event was `$emit`-ed or `$broadcast`-ed.
        *   - `currentScope` - {Scope}: the current scope which is handling the event.