[FIX] CorpusViewer: Don't Disable WebviewWidget for PyQt5

[nikicc]

Issue

In CorpusViewer scrolling didn't work on PyQt5.

Changes

Don't disable WebviewWidget when on PyQt5, since the issue will be solved in Orange. Blocked on biolab/orange3#1983.

[codecov-io]

Codecov Report

Merging #190 into master will increase coverage by 0.38%.

@@            Coverage Diff             @@
##           master     #190      +/-   ##
==========================================
+ Coverage      94%   94.38%   +0.38%     
==========================================
  Files          30       30              
  Lines        1567     1567              
  Branches      287      287              
==========================================
+ Hits         1473     1479       +6     
+ Misses         53       47       -6     
  Partials       41       41

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