fix bug in server-side 'group' definition
fix bug in server-side 'group' definition

In the docs, FlowRouter.group has only one options argument, but on the server it is created with 2 : 'path' and 'options'. By getting rid of the path argument, we get the expected behaviour on the server.
mquandalle/flow-router,dandv/flow-router,kadirahq/flow-router,katrotz/flow-router,elidoran/flow-router,mbernath/flow-router,VeliovGroup/flow-router,sprohaska/flow-router,meteorhacks/flow-router,bolus/flow-router,delgermurun/flow-router,richsilv/flow-router,frozeman/flow-router,alanning/flow-router