fix(encoding): take the first encoding supported

[ssoroka]

Browsers submit multiple supported encodings, such as
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

By the time this function gets the accept header encoding, the part after the ; has been removed, so we still need to split by , and find the first one we support.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.49%. Comparing base (b453166) to head (181b8c6).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #205   +/-   ##
=======================================
  Coverage   98.48%   98.49%           
=======================================
  Files          24       24           
  Lines         728      732    +4     
=======================================
+ Hits          717      721    +4     
  Misses          6        6           
  Partials        5        5           

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[abemedia]

Thanks for this! Would you mind adding a test though?

[ssoroka]

added tests and rebased master. Not sure why the CI checks aren't running.

[abemedia]

Looks good, thanks again!