Update tree-sitter-mozcpp to 0.20

[Luni-4]

This PR updates tree-sitter-mozcpp to 0.20
It fixes #579

[codecov-commenter]

Codecov Report

Merging #754 (bcd481b) into master (1c3c663) will decrease coverage by 0.06%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master     #754      +/-   ##
==========================================
- Coverage   39.19%   39.13%   -0.07%     
==========================================
  Files          51       51              
  Lines        6773     6805      +32     
  Branches      971      971              
==========================================
+ Hits         2655     2663       +8     
- Misses       3450     3473      +23     
- Partials      668      669       +1     

Impacted Files	Coverage Δ
src/checker.rs	72.50% <ø> (ø)
src/getter.rs	70.86% <ø> (+0.43%)	⬆️
src/languages/language_cpp.rs	3.40% <0.00%> (-0.18%)	⬇️
src/metrics/loc.rs	80.04% <87.50%> (+0.14%)	⬆️

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[marco-c]

Could you add the code from #579 as a test?