Fix for when GH_TOKEN is not set

[berquist]

The exception was never being thrown because GH_TOKEN was never None.

Accidentally introduced in 10e0f25.

[codecov-io]

Codecov Report

Merging #42 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #42   +/-   ##
=======================================
  Coverage   81.88%   81.88%           
=======================================
  Files           5        5           
  Lines         138      138           
=======================================
  Hits          113      113           
  Misses         25       25

Impacted Files	Coverage Δ
travis_sphinx/deploy.py	95% <100%> (ø)	⬆️

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[Syntaf]

Thanks for the typo fix, but why are you removing the default value of '' for the env variable? What would we gain from having a null instead of an empty string?

[berquist]

The empty string does not properly trigger this line, which leads to falling through to the message "Deploy triggered for non-master branch 'master': skipping deploy" and having the deploy return as successful.