Gmail - consecutive dots are not valid

[rathboma]

Fixes #818

While single dots in email addresses are ignored by Google, multiple consecutive dots are not, and in fact sending to an email with multiple dots inserted will result in a bounce.

Here is a speculative fix for that issue, with tests. It has one specific behavior that might be contentious, but I think may be the best balance:

On email normalization, it does NOT replace multiple consecutive dots, only single dots, regardless of the replace_dots option, because gmail itself doesn't do this behavior either.

[rathboma]

I've updated this to strip some un-needed gmail-specific logic from isEmail that in fact introduced a bug. Multiple consecutive dots in the user part of the email is invalid, regardless of domain. The gmail specific logic was causing this to be reported as valid.

See here for context:
https://serverfault.com/questions/395766/are-two-periods-allowed-in-the-local-part-of-an-email-address

I'm keeping the behavior in normalizeEmail to leave multiple consecutive dots in normalized gmail addresses as this is not something that gmail itself normalizes, so now you can call isEmail(normalizeEmail('multiple..dots@gmail.com')) and get the correct result.

[rathboma]

@chriso would love to get your take on this fix. I did add testing and we're using it in production right now at Kickbox.

[chriso]

Thanks for the PR, this looks correct.