auth: Fix client version not getting persisted

Gorm won't save changes to associated objects unless you use a
gorm.Session with FullSaveAssociations: true.

auth.go

@@ -161,7 +161,8 @@ func AuthAuthenticate(app *App) func(c echo.Context) error {
  }
  }
 
- result = app.DB.Save(&user)
+ // Save changes to user.Clients
+ result = app.DB.Session(&gorm.Session{FullSaveAssociations: true}).Save(&user)
  if result.Error != nil {
  return result.Error
  }