rest-api-accounts: Fix documentation of "Get Active" response

The endpoint actually returns a json content type response with the
Gerrit magic prefix ")]}'".

Change-Id: Ic810759b6277c055b282741a197904b5b9fde97e

Documentation/rest-api-accounts.txt

diff --git a/Documentation/rest-api-accounts.txt b/Documentation/rest-api-accounts.txt
index 6cb6e24..6421358 100644
--- a/Documentation/rest-api-accounts.txt
+++ b/Documentation/rest-api-accounts.txt
@@ -412,7 +412,10 @@
 .Response
 ----
   HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json; charset=UTF-8
 
+  )]}'
   ok
 ----