refactor!: Rename repo_dir to dir

[tony]

repo_dir param is renamed to dir:

Before: GitRepo(url='...', repo_dir='...')

After: GitRepo(url='...', dir='...')

[codecov]

Codecov Report

Merging #324 (2369a2d) into master (6c649bc) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #324   +/-   ##
=======================================
  Coverage   85.62%   85.62%           
=======================================
  Files          18       18           
  Lines         960      960           
=======================================
  Hits          822      822           
  Misses        138      138           

Impacted Files	Coverage Δ
libvcs/shortcuts.py	100.00% <ø> (ø)
tests/states/test_hg.py	95.23% <ø> (ø)
libvcs/states/base.py	100.00% <100.00%> (ø)
libvcs/states/git.py	76.77% <100.00%> (ø)
libvcs/states/hg.py	100.00% <100.00%> (ø)
libvcs/states/svn.py	64.51% <100.00%> (ø)
tests/states/test_base.py	100.00% <100.00%> (ø)
tests/states/test_git.py	99.38% <100.00%> (ø)
tests/states/test_svn.py	96.15% <100.00%> (ø)
tests/test_shortcuts.py	100.00% <100.00%> (ø)

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