Fix broken login after upgrade (#80)

* Added users(backend) field update

* dbVersion bumped to 6

backend/src/config/ConfigDefault.php

@@ -38,7 +38,7 @@ $defaultConfig = [
         ]
     ],
     'proxys' => [],
-    'dbVersion' => 5
+    'dbVersion' => 6
 ];
 
 if (file_exists('../config/ConfigOverride.php')) {

backend/src/sql/Update6.sql

@@ -0,0 +1,3 @@
+UPDATE users SET backend='native' WHERE backend='';
+
+UPDATE options SET value=6 WHERE name='schema_version';