Fix: rules.git_checkout not working with git 2.22.0

[ik1ne]

(.env) ik1nes-MacBook-Pro:~/Sources/thefuck ik1ne % git --version
git version 2.22.0
hub version 2.12.2
(.env) ik1nes-MacBook-Pro:~/Sources/thefuck ik1ne % thefuck --version
The Fuck 3.29 using Python 3.7.4 and ZSH 5.3
(.env) ik1nes-MacBook-Pro:~/Sources/thefuck ik1ne % git checkout mastr
error: pathspec 'mastr' did not match any file(s) known to git
(.env) ik1nes-MacBook-Pro:~/Sources/thefuck ik1ne % thefuck
Nothing found

As shown above, git 2.22.0 does not print period in its output so rules.git_checkout.match does not work with git 2.22.0.
So I removed the period in the string search.
Since it uses 'string' in command.output, previous version of git which prints period shouldn't be affected by this change. (tested the same command above inside git 2.17.2 and it works fine)

[ik1ne]

Added a new commit since exception with the same reason was happening to get_new_command.

[nvbn]

Looks good, thanks!