Update custom_godot_servers.rst

"but" doesn't seem correct in this context. I wonder how I missed this word.
Before: It is possible to emit signals to GDScript but calling the GDScript dummy object.
After: It is possible to emit signals to GDScript by calling the GDScript dummy object.

development/cpp/custom_godot_servers.rst

@@ -384,7 +384,7 @@ The dummy class binds singleton methods to GDScript. In most cases, the dummy cl
 
 Binding Signals
 
-It is possible to emit signals to GDScript but calling the GDScript dummy object.
+It is possible to emit signals to GDScript by calling the GDScript dummy object.
 
 .. code:: cpp