fix(isMail):fixed consecutive hyphen check in domain part

[kshavp]

When doing check with isEmail('[email protected]'), now returns false and behaves as expected. Fix based on suggestion by itbali

Fixes #2268

Checklist

• [x] PR contains only changes related; no stray files, etc.

• [x] README updated (where applicable)

• [x] Tests written (where applicable)

• [x] References provided in PR (where applicable)

[Daniyal-Qureshi]

Please add necessary test cases for this fix.