Merge branch '5.1' into 5.2

* 5.1:
  Update lockable_trait.rst

Author: OskarStark

console/lockable_trait.rst

@@ -38,6 +38,8 @@ that adds two convenient methods to lock and release commands::
             // if not released explicitly, Symfony releases the lock
             // automatically when the execution of the command ends
             $this->release();
+            
+            return 0;
         }
     }