Point to 7-0-stable in installation docs

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

doc/install/installation.md

@@ -141,12 +141,12 @@ We recommend using a PostgreSQL database. For MySQL check [MySQL setup guide](da
 ### Clone the Source
 
     # Clone GitLab repository
-    sudo -u git -H git clone https://gitlab.com/gitlab-org/gitlab-ce.git -b 6-9-stable gitlab
+    sudo -u git -H git clone https://gitlab.com/gitlab-org/gitlab-ce.git -b 7-0-stable gitlab
 
     # Go to gitlab dir
     cd /home/git/gitlab
 
-**Note:** You can change `6-9-stable` to `master` if you want the *bleeding edge* version, but never install master on a production server!
+**Note:** You can change `7-0-stable` to `master` if you want the *bleeding edge* version, but never install master on a production server!
 
 ### Configure it