Adding rubocop to travis pipelines

[alaxalves]

Fixes #548 (<=== Add issue number here)

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[codeclimate]

Code Climate has analyzed commit 950f02d6 and detected 0 issues on this pull request.

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[codecov]

Codecov Report

Merging #661 into main will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##             main     #661   +/-   ##
=======================================
  Coverage   41.36%   41.36%           
=======================================
  Files          34       34           
  Lines        1308     1308           
=======================================
  Hits          541      541           
  Misses        767      767

Impacted Files	Coverage Δ
app/models/map.rb	39% <100%> (ø)	⬆️

[alaxalves]

Already doing this at #672