Change build system to poetry

[kamil1b]

• update travis configuration
• add pre-hook for commit
• update tox config

[codecov]

Codecov Report

Merging #8 into master will decrease coverage by 33.34%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #8       +/-   ##
==========================================
- Coverage   34.61%   1.26%   -33.35%     
==========================================
  Files           2       3        +1     
  Lines          78      79        +1     
==========================================
- Hits           27       1       -26     
- Misses         51      78       +27

Impacted Files	Coverage Δ
src/git_taxbreak/__init__.py	100% <100%> (ø)
src/git_taxbreak/modules/argument_parser.py	0% <0%> (-34.79%)	⬇️
src/git_taxbreak/cmd.py	0% <0%> (-34.38%)	⬇️

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