Closes swcarpentry/styles#283
`site.email` is used as:
_includes/lesson_footer.html: <a href="mailto:{{ site.email }}">Contact</a>
_includes/workshop_footer.html: <a href="mailto:{{ site.email }}">Contact</a>
Therefore, it does not make sense to have `mailto` in the `email` itself.
# Overall title for pages.
title: "Lesson Title"
-# Contact. This *must* include the protocol: if it's an email
-# address, it must look like "mailto:lessons@software-carpentry.org",
-# or if it's a URL, "https://gitter.im/username/ProjectName".
-email: "mailto:lessons@software-carpentry.org"
+# Email address, no mailto:
+email: "lessons@software-carpentry.org"
#------------------------------------------------------------
# Generic settings (should not need to change).