update few usages of v1alpha1/v1beta1 to v1 (#2651)

Author: vaikas

docs/eventing/getting-started.md

@@ -245,7 +245,7 @@ events based on the Cloud Event context attributes.
 
    ```sh
    kubectl --namespace event-example apply --filename - << END
-   apiVersion: eventing.knative.dev/v1alpha1
+   apiVersion: eventing.knative.dev/v1
    kind: Trigger
    metadata:
      name: hello-display
@@ -269,7 +269,7 @@ events based on the Cloud Event context attributes.
 
    ```sh
    kubectl --namespace event-example apply --filename - << END
-   apiVersion: eventing.knative.dev/v1alpha1
+   apiVersion: eventing.knative.dev/v1
    kind: Trigger
    metadata:
      name: goodbye-display

docs/install/any-kubernetes-cluster.md

@@ -659,7 +659,7 @@ metadata:
   namespace: knative-eventing
 data:
   channelTemplateSpec: |
-    apiVersion: messaging.knative.dev/v1beta1
+    apiVersion: messaging.knative.dev/v1
     kind: InMemoryChannel
 ---
 apiVersion: v1