Travis update dist

[PrimozGodec]

Issue

Tests fail due to to many static dependencies.

Description of changes

As we did in other add-ons and in core Orange I am updating the dist to xenial.

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #67 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #67   +/-   ##
=======================================
  Coverage   79.21%   79.21%           
=======================================
  Files          17       17           
  Lines        2271     2271           
  Branches      278      278           
=======================================
  Hits         1799     1799           
  Misses        441      441           
  Partials       31       31

---

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (master@1b30b3f). Learn more about missing BASE report.
⚠️ Report is 246 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #67   +/-   ##
=========================================
  Coverage          ?   79.21%           
=========================================
  Files             ?       17           
  Lines             ?     2271           
  Branches          ?      278           
=========================================
  Hits              ?     1799           
  Misses            ?      441           
  Partials          ?       31           

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