Update nginx.md

Incorrect docker image used. (unable to start container process: exec: "htpasswd": executable file not found in $PATH: unknown.)

Author: another-pavels

registry/recipes/nginx.md

@@ -155,7 +155,7 @@ Review the [requirements](index.md#requirements), then follow these steps.
 3.  Create a password file `auth/nginx.htpasswd` for "testuser" and "testpassword".
 
     ```console
-    $ docker run --rm --entrypoint htpasswd registry:2 -Bbn testuser testpassword > auth/nginx.htpasswd
+    $ docker run --rm --entrypoint htpasswd httpd:2 -Bbn testuser testpassword > auth/nginx.htpasswd
     ```
 
     > **Note**: If you do not want to use `bcrypt`, you can omit the `-B` parameter.