Fix email validation regex

[vpasquino]

Pull Request Process

1. Ensure any install or build dependencies are removed before the end of the layer when doing a
   build.
2. Update the README.md with details of changes to the interface, this includes new environment
   variables, exposed ports, useful file locations and container parameters.
3. You may merge the Pull Request in once you have the sign-off of two other developers, or if you
   do not have permission to do that, you may request the second reviewer to merge it for you.