Fix typo on killall command.

In the official GitLab package for Ubuntu, gitlab-runner is symlinked to
gitlab-ci-multi-runner. When you attempt a killall command, you need to
type the latter.

docs/install/autoscaling.md

@@ -190,7 +190,7 @@ more in [Distributed runners caching][caching].
 1. Stop the Runner:
 
     ```bash
-    killall -SIGQUIT gitlab-runner
+    killall -SIGQUIT gitlab-ci-multi-runner
     ```
 
 1. Wait until the Runner exits. You can check its status with: `gitlab-runner status`