Add travis deploy key

[shilman]

Issue: #1131

What I did

Add travis deploy key to give travis the ability to push to gh-pages branch

How to test

N/A

[shilman]

Self-merging 👿

[codecov]

Codecov Report

Merging #1135 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1135   +/-   ##
=======================================
  Coverage   12.86%   12.86%           
=======================================
  Files         198      198           
  Lines        4501     4501           
  Branches      715      715           
=======================================
  Hits          579      579           
  Misses       3289     3289           
  Partials      633      633

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