Remove a period that can be annoying

I looked through the labels, not even `P1` or `customer+` was able to really capture the importance of this MR and what it means for the future of GitLab.

## What does this MR do?

It removes the period `.` at the end of the following line in the `Documentation` **Merge Request Template**

`See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html.`

## Why was this MR needed?

Because, while editing the MR `Description` the link is not clickable, so it is very easy to copy the link with the period `.` and then it ends up behaving like a broken link. I only realized that it was not a broken link because I was busy trying to find someone to fix the broken link.

See merge request !6890