Add check-docs-source-in-git to sanity.xml

[Prome88]

• Added check-docs-source-in-git to sanity.xml
• Removed Added check-docs-source-in-git from travis

[Prome88]

Apt install of graphviz & pydot instead of pip install is due to same issue as seen in WillKoehrsen/Data-Analysis#36

[codecov]

Codecov Report

Merging #1595 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1595   +/-   ##
=======================================
  Coverage   76.51%   76.51%           
=======================================
  Files         123      123           
  Lines        4564     4564           
  Branches      545      545           
=======================================
  Hits         3492     3492           
  Misses        900      900           
  Partials      172      172           

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