Fix error when specifying receiver outputs

gprMax/hash_cmds_multiuse.py

@@ -238,7 +238,7 @@ def process_multicmds(multicmds):
                 rx = Rx(
                     p1=(float(tmp[0]), float(tmp[1]), float(tmp[2])),
                     id=tmp[3],
-                    outputs=" ".join(tmp[4:]),
+                    outputs=tmp[4:],
                 )
 
             scene_objects.append(rx)