Update installing_agones.md

Added missing "\" at the end of command options.

docs/installing_agones.md

@@ -94,8 +94,8 @@ gcloud container clusters create [CLUSTER_NAME] --cluster-version=1.9 \
   --tags=game-server \
   --enable-basic-auth \
   --password=supersecretpassword \
-  --scopes=https://www.googleapis.com/auth/devstorage.read_only,compute-rw,cloud-platform
-  --num-nodes=3
+  --scopes=https://www.googleapis.com/auth/devstorage.read_only,compute-rw,cloud-platform \
+  --num-nodes=3 \
   --machine-type=n1-standard-1
 ```
 
@@ -231,4 +231,4 @@ That's it! This creates the [Custom Resource Definitions][crds] that power Agone
 
 * Go through the [Create a Game Server Quickstart][quickstart]
 
-[quickstart]: /docs/create_gameserver.md
+[quickstart]: /docs/create_gameserver.md