Update docs to use valid syntax. (hashicorp#1074)

Author: nat-henderson

docs/d/google_container_registry_image.html.markdown

@@ -15,12 +15,12 @@ The URLs are computed entirely offline - as long as the project exists, they wil
 ## Example Usage
 
 ```hcl
-data "google_container_registry_image" {
+data "google_container_registry_image" "debian" {
     name = "debian"
 }
 
 output "gcr_location" {
-    value = "${data.google_container_registry_image.image_url}"
+    value = "${data.google_container_registry_image.debian.image_url}"
 }
 ```
 

docs/d/google_container_registry_repository.html.markdown

@@ -15,10 +15,10 @@ The URLs are computed entirely offline - as long as the project exists, they wil
 ## Example Usage
 
 ```hcl
-data "google_container_registry_repository" {}
+data "google_container_registry_repository" "foo" {}
 
 output "gcr_location" {
-    value = "${data.google_container_registry_repository.repository_url}"
+    value = "${data.google_container_registry_repository.foo.repository_url}"
 }
 ```