Replace valid email domains with .invalid TLDs

Description of the Change

Replaces valid, functioning third-party email addresses with ones that do not have a resolvable TLD. The .invalid TLD is reserved by IETF in BCP 32/RFC 2606 and will never route.

  ".invalid" is intended for use in online construction of domain
 names that are sure to be invalid and which it is obvious at a
 glance are invalid.

Closes #

Alternate Designs

An alternate design would be to replace these domain names with a dedicated domain name that is owned by 10up.

Possible Drawbacks

Errors may be thrown by WordPress if WordPress tries to send mail to these servers.

Verification Process

Unverified.

To verify, check out this branch and create a snasphot using it, then load the snapshot and verify that all users have email addresses with .invalid as the TLD.

Checklist:

[x] I have read the CONTRIBUTING document.
[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[ ] I have added tests to cover my change.
[ ] All new and existing tests passed.

10up / wpsnapshots