fixed demo challenge commands

ps-grammar/demoChallenge/commands.jsgf

@@ -5,6 +5,6 @@ public <statement> = [tobi] [please] <command> [please] [tobi];
 <command> =  <mapping> | <clean> | <party> | <teach>;
 <clean> = (clean up) | (start cleaning);
 <mapping> = ( start mapping );
-<party> = ( [the] party starts) | (party beginning) | (party starting)  | (lets start the party);
+<party> = ( start the party ) | (lets party) | (party starting)  | (lets start the party);
 <teach> = ( (this is [a | an | the] ) | ( these are [the] ) ) <object>;
 <object> = trashbin;