Fix websocket test script

Unclear when or why this changed in python, but doesn't really matter.
Fix the script.

Tested: Script now succeeds with rest option enabled.

Change-Id: I3e548aad03c6150f404d5fddc742f8baa5274a83
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/scripts/websocket_test.py b/scripts/websocket_test.py
index fce9cd7..ef58a59 100755
--- a/scripts/websocket_test.py
+++ b/scripts/websocket_test.py
@@ -46,7 +46,7 @@
     auth = "Basic {}".format(base64.b64encode(authbytes).decode("ascii"))
     headers = {"Authorization": auth}
     async with (
-        websockets.connect(uri, ssl=ssl_context, extra_headers=headers)
+        websockets.connect(uri, ssl=ssl_context, additional_headers=headers)
         if args.ssl
         else websockets.connect(uri, extra_headers=headers)
     ) as websocket: