Unpin karma-webpack version

[gdetrez]

See codymikol/karma-webpack#284 for background.

[codecov-io]

Codecov Report

Merging #306 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #306      +/-   ##
==========================================
+ Coverage   37.79%   37.83%   +0.04%     
==========================================
  Files         168      168              
  Lines       16391    16391              
  Branches     2908     2908              
==========================================
+ Hits         6195     6202       +7     
+ Misses       9771     9767       -4     
+ Partials      425      422       -3

Impacted Files	Coverage Δ
scanomatic/data_processing/phases/segmentation.py	74.58% <0%> (+1.95%)	⬆️

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[coveralls]

Coverage increased (+0.04%) to 43.061% when pulling 30f24be on gdetrez:unpin-karma-webpack into fcfc6ab on Scan-o-Matic:master.