filters/git_last_checkout_spec: support subdomains in e-mail regex
filters/git_last_checkout_spec: support subdomains in e-mail regex

This test will not pass if your email includes a subdomain. The new regexp
enables subdomain support.

```
[5] pry(main)> "a@a.b.com".match(/\A\w+[\w.-]*@(\w+\.)+\w+\z/)
=> #<MatchData "a@a.b.com" 1:"b.">
[6] pry(main)> "a@com".match(/\A\w+[\w.-]*@(\w+\.)+\w+\z/)
=> nil
[7] pry(main)> "a@foo.com".match(/\A\w+[\w.-]*@(\w+\.)+\w+\z/)
=> #<MatchData "a@foo.com" 1:"foo.">
```

Thanks to: @derSascha

airbrake/airbrake-ruby,airbrake/airbrake-ruby