fix installation from source

[PetrDlouhy]

Fix #170

[codecov[bot]]

Codecov Report

Merging #171 (c3e1502) into master (0f09d7d) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #171   +/-   ##
=======================================
  Coverage   64.97%   64.97%           
=======================================
  Files          24       24           
  Lines        1122     1122           
  Branches      248      248           
=======================================
  Hits          729      729           
  Misses        299      299           
  Partials       94       94           

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[PetrDlouhy]

There seems to be no issue in current master with this.