fix(git): fix returned value for GitCommit.message when body is empty

[vBLFTePebWNi6c]

GitCommit.message should return only title without excess newlines if commit body is empty.

[codecov]

Codecov Report

Merging #166 into master will increase coverage by 0.31%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   91.53%   91.84%   +0.31%     
==========================================
  Files          33       33              
  Lines         768      785      +17     
==========================================
+ Hits          703      721      +18     
+ Misses         65       64       -1     

Flag	Coverage Δ
#unittests	91.84% <100.00%> (+0.31%)	⬆️

Impacted Files	Coverage Δ
commitizen/git.py	95.00% <100.00%> (ø)
commitizen/config/__init__.py	81.81% <0.00%> (-0.80%)	⬇️
commitizen/cz/customize/customize.py	84.78% <0.00%> (-0.22%)	⬇️
commitizen/cz/base.py	100.00% <0.00%> (ø)
commitizen/defaults.py	100.00% <0.00%> (ø)
commitizen/cz/__init__.py	100.00% <0.00%> (ø)
commitizen/error_codes.py	100.00% <0.00%> (ø)
commitizen/cz/jira/jira.py	100.00% <0.00%> (ø)
...en/cz/conventional_commits/conventional_commits.py	100.00% <0.00%> (ø)
commitizen/config/base_config.py	91.66% <0.00%> (+0.36%)	⬆️
... and 2 more

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[Lee-W]

Thanks for contributing 🎉

[Lee-W]

Nice! Let's merge it 👍

[woile]

Awesome!