Improve compatibility with older git versions

[pilou-]

--no-patch was added in Git 1.8.4 and is a synonym for -s. Fixes #31

[codecov-io]

Codecov Report

Merging #36 into master will not change coverage. The diff coverage is 100%.

@@         Coverage Diff          @@
##           master   #36   +/-   ##
====================================
  Coverage      99%   99%           
====================================
  Files           9     9           
  Lines         909   909           
  Branches      178   176    -2     
====================================
  Hits          900   900           
  Misses          4     4           
  Partials        5     5

Impacted Files	Coverage Δ
sphinxcontrib/versioning/git.py	98.09% <100%> (ø)	:white_check_mark:

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