Updating CDN link to use @2.1.0

[github-actions]

Compiled JS files from last release are here:

https://cdn.jsdelivr.net/gh/atk4/ui@2.1.0/public/

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update some of our documentation based on your changes.

[codecov]

Codecov Report

Merging #1038 into develop will increase coverage by 0.02%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop    #1038      +/-   ##
=============================================
+ Coverage      71.59%   71.61%   +0.02%     
  Complexity      2655     2655              
=============================================
  Files            126      126              
  Lines           6181     6179       -2     
=============================================
  Hits            4425     4425              
+ Misses          1756     1754       -2     

Impacted Files	Coverage Δ	Complexity Δ
src/App.php	78.91% <ø> (ø)	138.00 <0.00> (ø)
src/TableColumn/Generic.php	84.53% <0.00%> (+0.86%)	38.00% <0.00%> (ø%)
src/ItemsPerPageSelector.php	68.96% <0.00%> (+2.29%)	11.00% <0.00%> (ø%)

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