remove extra slash (docker#2516)

Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

Author: andrewhsu

engine/installation/linux/debian.md

@@ -222,7 +222,7 @@ If you cannot use Docker's repository to install Docker CE, you can download the
 `.deb` file for your release and install it manually. You will need to download
 a new file each time you want to upgrade Docker.
 
-1.  Go to [{{ download-url-base }}/dists//]({{ download-url-base }}/dists/),
+1.  Go to [{{ download-url-base }}/dists/]({{ download-url-base }}/dists/),
     choose your Ubuntu version, browse to `stable/pool/stable/amd64/`, and
     download the `.deb` file for the Docker version you want to install and for
     your version of Debian.