feat: Add semantic release

[idirouhab]

Fixing issue #2

To make it work, a new GitHub token must be added to Travis

the new environment variables must be called either GITHUB_TOKEN or GH_TOKEN
How to create a new Github token: https://help.github.com/articles/creating-a-personal-access-token-for-the-command-line/

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master      #3   +/-   ##
======================================
  Coverage    82.6%   82.6%           
======================================
  Files           2       2           
  Lines          23      23           
======================================
  Hits           19      19           
  Misses          2       2           
  Partials        2       2

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[aperezg]

Seems an interesting proposal, we'll take a look :)