cherry_picker doesn't support forward-porting to master

[larryhastings]

% cherry_picker <hash> master caused cascading exceptions:

Traceback (most recent call last):
File "/home/larry/lib/python3.7/site-packages/cherry_picker/cherry_picker.py", line 463, in version_from_branch
return tuple(map(int, re.match(r'^.(?P\d+(.\d+)+).$', branch).groupdict()['version'].split('.')))
AttributeError: 'NoneType' object has no attribute 'groupdict'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/home/larry/bin/cherry_picker", line 11, in
sys.exit(cherry_pick_cli())
File "/home/larry/lib/python3.7/site-packages/click/core.py", line 722, in call
return self.main(*args, **kwargs)
File "/home/larry/lib/python3.7/site-packages/click/core.py", line 697, in main
rv = self.invoke(ctx)
File "/home/larry/lib/python3.7/site-packages/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/larry/lib/python3.7/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/home/larry/lib/python3.7/site-packages/cherry_picker/cherry_picker.py", line 412, in cherry_pick_cli
cherry_picker.backport()
File "/home/larry/lib/python3.7/site-packages/cherry_picker/cherry_picker.py", line 269, in backport
for maint_branch in self.sorted_branches:
File "/home/larry/lib/python3.7/site-packages/cherry_picker/cherry_picker.py", line 81, in sorted_branches
key=version_from_branch)
File "/home/larry/lib/python3.7/site-packages/cherry_picker/cherry_picker.py", line 465, in version_from_branch
raise ValueError(f'Branch {branch} seems to not have a version in its name.') from attr_err
ValueError: Branch master seems to not have a version in its name.

[Mariatta]

GitMate.io thinks possibly related issues are #149 (pip install does not work for cherry_picker), #270 (Teach cherry_picker to forwardport to master), #140 (Move cherry_picker over to flit), python/blurb#2 (blurb does not support command line options in EDITOR/GIT_EDITOR), and python/devguide#3 (Add Travis support).

[larryhastings]

GitMate.io is right, this is a duplicate of #270.