fix(docs): add missing options synthax on isISO8601 validator

[leonardovillela]

This PR update the README.md docs to include the missing options optional parameter on isISO8601 validator.

Checklist

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

[codecov]

Codecov Report

Merging #1860 (a97d726) into master (47ee5ad) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1860   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          102       102           
  Lines         2059      2059           
  Branches       464       464           
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  Hits          2059      2059           

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[tux-tn]

LGTM 🎉 Thank you for your PR @leonardovillela

[leonardovillela]

Thank you very much, I'm happy to contribute (even though is a small change).

Can you send me more issues to work? :)

[tux-tn]

Thank you for your enthusiasm and interest in this project!
Feel free to contribute by adding a missing locale in one of our validators (See #1761 as an example) or fix an open issue if nobody has not already opened a PR for it.

[profnandaa]

Thanks for your contrib! 🎉