Explicitly set character encoding for locustfile downloaded from master.

Author: cyberw

Diff for: locust/argument_parser.py

@@ -293,7 +293,7 @@ def wait_for_reply():
         sys.exit(1)
 
     filename = msg.data["filename"]
-    with open(os.path.join(tempfile.gettempdir(), filename), "w") as locustfile:
+    with open(os.path.join(tempfile.gettempdir(), filename), "w", encoding="utf-8") as locustfile:
         locustfile.write(msg.data["contents"])
 
     def exit_handler():