Fix broken link to GCP Resource Manager's folder API doc. (hashicorp#562)

Author: ubschmidt2

website/docs/r/google_folder.html.markdown

@@ -11,7 +11,7 @@ description: |-
 Allows management of a Google Cloud Platform folder. For more information see 
 [the official documentation](https://cloud.google.com/resource-manager/docs/creating-managing-folders)
 and 
-[API](https://cloud.google.com/resource-manager/reference/rest/v2/folder).
+[API](https://cloud.google.com/resource-manager/reference/rest/v2/folders).
 
 A folder can contain projects, other folders, or a combination of both. You can use folders to group projects under an organization in a hierarchy. For example, your organization might contain multiple departments, each with its own set of Cloud Platform resources. Folders allows you to group these resources on a per-department basis. Folders are used to group resources that share common IAM policies.