Note: This is a breaking change. The order of parameters of `PullRequest.get_review_comments` has changed to match other `get_comments` methods and Github API parameter order. Users should change `PullRequest.get_review_comments(since)` to `PullRequest.get_review_comments(since=since)`.
Calling without parameter is not breaking: `PullRequest.get_review_comments()`
* PullRequest.update_branch(): allow expected_head_sha to be empty
* PullRequest.testUpdateBranch(): test also with empty expected_head_sha
* Updated replay data for PullRequest.testUpdateBranch
* tox formatted changes
* Add Support for PullRequest update-branch
* Add test case
* Fix test case
* Add test data record
* Update PullRequest.py
* Update PullRequest.py
* Support py2.7
* Assert response status is 202
* black + isort