fix typo

README.md

@@ -159,7 +159,7 @@ web-path | path to static web files (for development or custom front end) | |
 proxy-path | path prefix when service is run behind a proxy | |
 ga-key | google analytics key for the front end | |
 uservoice-key | user voice key for the front end  | |
-provider | which storage provider to use | (s3, grdrive or local) |
+provider | which storage provider to use | (s3, gdrive or local) |
 aws-access-key | aws access key | | AWS_ACCESS_KEY
 aws-secret-key | aws access key | | AWS_SECRET_KEY
 bucket | aws bucket | | BUCKET