[Minor] fix periods in headers

Currently we have six files that have technically invalid headers, as
the trailing period is required by presubmit.

This patch fixes all current instances of this issue.

Change-Id: Icaee3034cd89dcfc65061e37df5097b7fbc1ad4c
Reviewed-on: https://chromium-review.googlesource.com/c/openscreen/+/2443930
Reviewed-by: Ryan Keane <rwkeane@google.com>
Commit-Queue: Jordan Bayles <jophba@chromium.org>
diff --git a/platform/api/udp_socket.cc b/platform/api/udp_socket.cc
index 2da7a73..47eba8b 100644
--- a/platform/api/udp_socket.cc
+++ b/platform/api/udp_socket.cc
@@ -1,6 +1,6 @@
 // Copyright 2019 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file
+// found in the LICENSE file.
 
 #include "platform/api/udp_socket.h"