twitter-server: fix json in doc of Admin.rst
twitter-server: fix json in doc of Admin.rst

Summary: Problem

closing bracket is missing.

Solution

add closing bracket.

Result

it will be valid json.

Signed-off-by: Kevin Oliver <koliver@twitter.com>

Differential Revision: https://phabricator.twitter.biz/D70198

twitter/twitter-server,twitter/twitter-server,twitter/twitter-server