fix: Properly parse meta tag when parameters are reversed

[dsuket]

convertBodyfunction work fine when html has this meta tag.
<meta http-equiv="content-type" content="text/html;charset=shift_jis">

However, if the http-equiv attribute is reversed like this, it will not work.
<meta content="text/html; charset=Shift_JIS" http-equiv="Content-Type" />

[codecov-io]

Codecov Report

Merging #682 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #682   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           7      7           
  Lines         575    579    +4     
  Branches      183    185    +2     
=====================================
+ Hits          575    579    +4

Impacted Files	Coverage Δ
src/body.js	100% <100%> (ø)	⬆️

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[Richienb]

In v3, we are going to be replacing the regex system with an actual parser in Richienb/fetch-charset-detection/src/index.ts#L53 but we can still use this as a band-aid patch if we do eventually make a final release for v2.

I'm adding some unit tests now.

[dsuket]

@Richienb Thank you for your reply.
Added test. I'm sorry if it's misplaced.