[RFC] Fix month calculation between dates

[rntdrts]

Fixes #69

[codecov]

Codecov Report

Merging #77 (a94c614) into master (ce063dd) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
+ Coverage   89.11%   89.18%   +0.07%     
==========================================
  Files           3        3              
  Lines         634      629       -5     
==========================================
- Hits          565      561       -4     
  Misses         44       44              
+ Partials       25       24       -1     

Impacted Files	Coverage Δ
carbon.go	90.21% <100.00%> (-0.25%)	⬇️
translator.go	65.51% <100.00%> (+6.89%)	⬆️

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