Lower the role name before using it

Signed-off-by: Joas Schilling <coding@schilljs.com>

lib/private/Setup/PostgreSQL.php

@@ -60,7 +60,7 @@ class PostgreSQL extends AbstractDatabase {
 				//use the admin login data for the new database user
 
 				//add prefix to the postgresql user name to prevent collisions
-				$this->dbUser = 'oc_' . $username;
+				$this->dbUser = 'oc_' . strtolower($username);
 				//create a new password so we don't need to store the admin config in the config file
 				$this->dbPassword = \OC::$server->getSecureRandom()->generate(30, \OCP\Security\ISecureRandom::CHAR_LOWER . \OCP\Security\ISecureRandom::CHAR_DIGITS);