Make sure you have given the below format in th/etc/mongod.conf for security option as you have made an mistake in security option.
security:
authorization: 'enabled' -----> to enable authentication
authentication: 'disabled' -------> to disable the authentication

if you dont want to secure your MongoDb database,just comment this security directive in /etc/mongod.conf

Note:

Ensure there exists an white space between the authorization and 'enabled',only then the service of mongoDB will run successfully.