Fix bug in change streamer

Tested on local instance of couch. include_docs parameter values “True” and “False” apparently both evaluate to false since neither value causes the docs to be included. A value of “true” causes them to be included.

http://127.0.0.1:5984/commcarehq/_changes?include_docs=True - not included
http://127.0.0.1:5984/commcarehq/_changes?include_docs=true - included

@czue @snopoke