Fix PDF generation with Sphinx

[amotl]

Hi there,

this tries to improve the situation with #155. make latexpdf now works again.

Cheers,
Andreas.

[codecov]

Codecov Report

Merging #160 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #160   +/-   ##
=======================================
  Coverage   91.85%   91.85%           
=======================================
  Files          28       28           
  Lines        1436     1436           
  Branches      103      103           
=======================================
  Hits         1319     1319           
  Misses         88       88           
  Partials       29       29           

Flag	Coverage Δ
#unittests	91.85% <ø> (ø)

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