use vtkmodules import instead of vtk

[darrellenns]

fixes #915

[codecov]

Codecov Report

Merging #918 (1e6e20b) into master (930ceb9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #918   +/-   ##
=======================================
  Coverage   95.94%   95.94%           
=======================================
  Files          32       32           
  Lines        7825     7827    +2     
  Branches      846      846           
=======================================
+ Hits         7508     7510    +2     
  Misses        184      184           
  Partials      133      133           

Impacted Files	Coverage Δ
cadquery/occ_impl/assembly.py	96.03% <100.00%> (ø)
cadquery/occ_impl/exporters/assembly.py	100.00% <100.00%> (ø)
cadquery/occ_impl/exporters/vtk.py	100.00% <100.00%> (ø)
cadquery/occ_impl/shapes.py	92.70% <100.00%> (+<0.01%)	⬆️

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[jmwright]

Thanks @darrellenns