Update CI pipeline to use Github Actions

[artursmet]

Travis CI pipeline looks outdated, this PR adds github actions pipeline instead

[codecov[bot]]

Codecov Report

Merging #40 (9a45839) into master (985d909) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   99.40%   99.39%   -0.02%     
==========================================
  Files           8        7       -1     
  Lines         338      330       -8     
  Branches       54       54              
==========================================
- Hits          336      328       -8     
  Misses          1        1              
  Partials        1        1              

Impacted Files	Coverage Δ
prices/discount.py	94.28% <100.00%> (ø)
prices/__init__.py

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[artursmet]

@NyanKiyoshi I've addressed your concerns