fix(isFQDN): allow_numeric_tld option didn't work

[BigOsvaap]

According to the mentioned on this comment #1923 (comment)

Example: abc.efg.g1h. will always fail, current options don't provide this use case, but is valid

validator.isFQDN('abc.efg.g1h.', 
  { allow_trailing_dot: true, allow_underscores: true, allow_numeric_tld: true}); // false but should be true

the option allow_numeric_tld didn't work as supposed to do, this PR tries to fix that.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

Merging #1939 (c605fe6) into master (c1b21a9) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1939   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          102       102           
  Lines         2085      2085           
  Branches       472       472           
=========================================
  Hits          2085      2085           

Impacted Files	Coverage Δ
src/lib/isFQDN.js	100.00% <100.00%> (ø)

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