Get upcoming meetups from API user instead of by parameter.

[alabeduarte]

This issue is about adding the ability to get upcoming meetups according to the groups which the API user belongs to, so whenever a user joins a new group there will no need for adding a new argument to the service.

Current way:

$ make run meetupName=Ruby-On-Rails-Oceania-Sydney

Expected way:

$ make run

or just: npm start