Add CDNJS version badge in README.md

[extend1994]

This badge will show the library latest version on CDNJS!

[codecov-io]

Codecov Report

Merging #11 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #11   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          70     70           
  Branches       25     25           
=====================================
  Hits           70     70

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