Added "exclude_repo" option to Top Langs

[Bas950]

As requseted in #480
Making different PRs for the new features

/api/top-langs/?username=USER

/api/top-langs/?username=USER&exclude_repo=REPO

Will make PRs for the other features after this one is merged, otherwise we will get merge conflicts.

[codecov]

Codecov Report

Merging #493 into master will decrease coverage by 0.06%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
- Coverage   92.25%   92.19%   -0.07%     
==========================================
  Files          20       20              
  Lines         581      589       +8     
  Branches      161      162       +1     
==========================================
+ Hits          536      543       +7     
- Misses         39       40       +1     
  Partials        6        6              

Impacted Files	Coverage Δ
src/fetchers/top-languages-fetcher.js	97.29% <88.88%> (-2.71%)	⬇️
api/top-langs.js	94.11% <100.00%> (ø)

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[aeris170]

MERGE THIS

[anuraghazra]

Thanks @Bas950