Fix link in patch update guide

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/).