update launch.py (#58)

update launch.py for supporting the case in which one wanna run multi accelerate instances in single node multigpu. avoiding the port conflict.

src/accelerate/commands/launch.py

@@ -137,6 +137,7 @@ def multi_gpu_launcher(args):
         )
     else:
         cmd.extend(["--nproc_per_node", str(args.num_processes)])
+        cmd.extend(["--master_port", str(args.main_process_port)])
     cmd.append(args.training_script)
     cmd.extend(args.training_script_args)