Fix grid header columns

[herflis]

No description provided.

[sensenet]

Site name	Url	Last deploy
sn-react-component-docs-dev	https://5f57b5eecf09624607c1a383--sn-react-component-docs-dev.netlify.app	Tue Sep 08 2020 - 16:49:08 GMT+0000 (Coordinated Universal Time)
sn-app-dev	https://5f57b5e94eef783fede58d5f--sn-app-dev.netlify.app	Tue Sep 08 2020 - 16:48:42 GMT+0000 (Coordinated Universal Time)

[codecov]

Codecov Report

Merging #846 into develop will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #846   +/-   ##
========================================
  Coverage    92.54%   92.54%           
========================================
  Files          217      217           
  Lines         5874     5875    +1     
  Branches      1506     1507    +1     
========================================
+ Hits          5436     5437    +1     
  Misses         438      438           

Impacted Files	Coverage Δ
...ntrols-react/src/ContentList/virtualized-table.tsx	98.92% <100.00%> (+0.01%)	⬆️

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