docs(isMACAddress): improve ambiguous option description

[stoneLeaf]

Improve ambiguous isMACAddress() option description

The no_separators option of the isMACAddress() validator will make it only check MAC addresses without separators.
Whereas the doc is ambiguously stating that it "allows" them, leaving unclear the fact that it would reject addresses with separators.

Checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3847c6f) to head (b1a1a91).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2563   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2535      2535           
  Branches       641       641           
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  Hits          2535      2535           

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