Fix get_hashes returning a non existing key

[cblegare]

Should fix #407

[codecov]

Codecov Report

Merging #408 (177c288) into master (17c2384) will decrease coverage by 0.25%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #408      +/-   ##
==========================================
- Coverage   94.24%   93.98%   -0.26%     
==========================================
  Files          11       11              
  Lines        1164     1114      -50     
==========================================
- Hits         1097     1047      -50     
  Misses         67       67              

Impacted Files	Coverage Δ
pyup/requirements.py	87.61% <0.00%> (-0.85%)	⬇️
pyup/pullrequest.py	96.77% <0.00%> (-0.45%)	⬇️
pyup/providers/gitlab.py	85.12% <0.00%> (-0.13%)	⬇️
pyup/bot.py	97.83% <0.00%> (-0.05%)	⬇️
pyup/config.py	98.92% <0.00%> (-0.02%)	⬇️
pyup/providers/github.py	99.39% <0.00%> (-0.01%)	⬇️
pyup/updates.py	100.00% <0.00%> (ø)

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[cblegare]

Looks like backward incompatible change from pygithub broke the build

PyGithub/PyGithub#1887

Are you not using Pyup? 😉

[cblegare]

duplicate of #392