Fix syntax of Knative install command (#736)

Author: Freakin

install/Knative-with-GKE.md

@@ -165,9 +165,9 @@ your Knative installation, see [Performing a Custom Knative Installation](Knativ
 
 1. Run the `kubectl apply` command to install Knative and its dependencies:
     ```bash
-    kubectl apply --filename https://github.com/knative/serving/releases/download/v0.2.3/release.yaml /
-    --filename https://github.com/knative/eventing/releases/download/v0.2.1/eventing.yaml /
-    --filename --filename https://github.com/knative/eventing-sources/releases/download/v0.2.1/release.yaml
+    kubectl apply --filename https://github.com/knative/serving/releases/download/v0.2.3/release.yaml \
+    --filename https://github.com/knative/eventing/releases/download/v0.2.1/eventing.yaml \
+    --filename https://github.com/knative/eventing-sources/releases/download/v0.2.1/release.yaml
     ```
 1. Monitor the Knative components until all of the components show a
    `STATUS` of `Running`: