Merge branch 'fix-upgrade-guide' into 'master'

Fix link in patch update guide

Use an absolute URL to gitlab.com's master branch instead of a relative URL on the local instance.  Also change which words are include in the anchor element, since the Markdown parser doesn't seem to like backticks inside the link text.

### Before

![update_link_before](https://dev.gitlab.org/Okada/gitlabhq/uploads/f6a8b2aa06ca210d5ea8a8b28a78c30c/update_link_before.png)

### After

![update_link_after](https://dev.gitlab.org/Okada/gitlabhq/uploads/6df92b3f5d8ffd6906bdc62cf19acb11/update_link_after.png)

cc @sytse

See merge request !1735

CHANGELOG

@@ -5,6 +5,7 @@ v 7.10.0 (unreleased)
   - Fix cross references when usernames, milestones, or project names contain underscores (Stan Hu)
   - enable line wrapping per default and remove the checkbox to toggle it (Hannes Rosenögger)
   - extend the commit calendar to show the actual commits made on a date (Hannes Rosenögger)
+  - Fix a link in the patch update guide
   - Add a service to support external wikis (Hannes Rosenögger)
   - List new commits for newly pushed branch in activity view.
   - Add changelog, license and contribution guide links to project sidebar.

doc/update/patch_versions.md

 # Universal update guide for patch versions
-*Make sure you view this [upgrade guide from the `master` branch](../../../master/doc/update/patch_versions.md) for the most up to date instructions.*
+*Make sure you view this [upgrade guide](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/update/patch_versions.md) from the `master` branch for the most up to date instructions.*
 
 For example from 6.2.0 to 6.2.1, also see the [semantic versioning specification](http://semver.org/).