fix typos of source comments at lib/redmine/hook.rb

git-svn-id: http://svn.redmine.org/redmine/trunk@13068 e93f8b46-1217-0410-a6f0-8f06a7374b81

Author: marutosi

lib/redmine/hook.rb

@@ -30,12 +30,12 @@ def add_listener(klass)
         clear_listeners_instances
       end
 
-      # Returns all the listerners instances.
+      # Returns all the listener instances.
       def listeners
         @@listeners ||= @@listener_classes.collect {|listener| listener.instance}
       end
 
-      # Returns the listeners instances for the given hook.
+      # Returns the listener instances for the given hook.
       def hook_listeners(hook)
         @@hook_listeners[hook] ||= listeners.select {|listener| listener.respond_to?(hook)}
       end