release v2.11.0

This is the first new release after moving dex from github.com/coreos to
github.com/dexidp. In the process, a new Quay repository was created, so
you can find the official docker image for this release at:

    quay.io/dexidp/dex:v2.11.0

Note that every merge to master now results in a docker image built in
that repository, making it easier to consume recent code changes, and
allowing for a more automated release process.

Features:

- Updates go to 1.10.2 to support SHA-512 for ldaps (@kpschuck, #1233)
- Fix timeout bug for etcd3 client connect (byxorna, #1266)
- Fix default baseURL for GitLab connector (@AnianZ, #1279)
- Connectors/ldap: treat 'constraint violation' on bind as bad
  credentials (@srenatus, #1285)

...and many fixes to the documentation and examples. Thank you, everyone
involved in helping out here.