After this commit, dev auth would start working with the `REMARK_URL`
hostname instead of the previously hardcoded 127.0.0.1.
Breaks development setup where `REMARK_URL` was set
to a non-standard value and dev auth was running on 127.0.0.1
and working, as, after that change, it would stop working.
In #1359, we discovered that StartTLS was not working\
due to the wrong host passed. This bumps the library for the fix.
Also, after a switch to go-pkgz/notify MailGun email sending
broke due to the difference in the destination email parsing,
the fix is also applied after this commit.
Dmitry Verkhoturov
