Update bitly_api/bitly_api.py

Fix duplicate function name "bundle_collaborator_remove".
Update user_link_history

* Use "on", "off", "both" instead of invalid booleans
* Add private option, which also uses "on", "off", "both" options
Merge pull request #16 from yasar11732/master

Fix function name for bundle pending collaborator removal.
Merge pull request #18 from jphines/user_link_history_18

Outdated user_link_history