Remove html language

[Luni-4]

Html language wasn't used for any kind of metric, so it is better to remove it

[codecov-io]

Codecov Report

Merging #360 (ced8e91) into master (d893d07) will increase coverage by 0.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
+ Coverage   22.35%   22.58%   +0.23%     
==========================================
  Files          46       45       -1     
  Lines        5722     5663      -59     
  Branches      813      808       -5     
==========================================
  Hits         1279     1279              
+ Misses       3913     3854      -59     
  Partials      530      530              

Impacted Files	Coverage Δ
src/alterator.rs	32.46% <ø> (+4.68%)	⬆️
src/checker.rs	36.36% <ø> (ø)
src/getter.rs	48.48% <ø> (ø)
src/langs.rs	90.00% <ø> (ø)
src/metrics/cognitive.rs	51.59% <ø> (ø)
src/metrics/cyclomatic.rs	56.96% <ø> (ø)
src/metrics/exit.rs	58.82% <ø> (ø)
src/metrics/fn_args.rs	64.40% <ø> (ø)
src/metrics/halstead.rs	48.38% <ø> (ø)
src/metrics/loc.rs	58.73% <ø> (ø)
... and 4 more

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