Strip whitespace when reading API token

[cjolowicz]

It is a common error to paste the PAT with a space at the end. The program does not strip this space and stores the token as-is in its cache. Currently this results in an error whenever the token is used:

⨯ The command git push failed with status 128.

❯ git push 'https://******************************** :[email protected]/cjolowicz/cookiecutter-hypermodern-python.git' +retrocookie-pr/poetry-up/babel-2.9.1

remote: Support for password authentication was removed on August 13, 2021. Please use a personal access token instead.
remote: Please see https://github.blog/2020-12-15-token-authentication-requirements-for-git-operations/ for more information.
fatal: Authentication failed for 'https:/cjolowicz/cookiecutter-hypermodern-python.git/'