ChainedSelectMultiple widget doesnt update css on override

[DARKDEYMON]

ChainedSelectMultiple doesn't update de css extra attrs
attrs.update(self.attrs)##< this is missing
attrs["data-chainfield"] = chain_field
attrs["data-url"] = url

[codecov]

Codecov Report

Merging #349 (b8457fd) into master (04a26ef) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #349      +/-   ##
==========================================
+ Coverage   80.42%   80.46%   +0.04%     
==========================================
  Files           8        8              
  Lines         470      471       +1     
  Branches       81       68      -13     
==========================================
+ Hits          378      379       +1     
  Misses         60       60              
  Partials       32       32              

Impacted Files	Coverage Δ
smart_selects/widgets.py	66.48% <100.00%> (+0.18%)	⬆️

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