ghMentions does not work with username having dots

Description

In GitLab, dots are allowed in usernames (unlike in GitHub). When using ghMentions with ghMentionsLink, if the given username contains a dot, the link is made only with what is before the dot.

Input

@john.doe

With the following showdown options:

{
    ghMentions: true,
    ghMentionsLink: 'https://gitlab.example.com/{u}',
}

Expected output

<a href="https://gitlab.example.com/john.doe>@john.doe</a>

Actual output

<a href="https://gitlab.example.com/john>@john</a>.doe

[davidsandoz]

Done 😉

[tivie]

I will make showdown allow dashes, underscores and dots in the middle of the username, since that seems a valid usecase scenario