cosmetics: trim trailing whitespace

When the license headers were updated, they accidentally contained
trailing whitespace, so unfortunately we have to touch all the files
again.

Change-Id: I236c05fade06589e417179c0444cb39b09e4200d

docs.mk

diff --git a/docs.mk b/docs.mk
index f60a482..f90d157 100644
--- a/docs.mk
+++ b/docs.mk
@@ -1,10 +1,10 @@
 ##
 ##  Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
 ##
-##  Use of this source code is governed by a BSD-style license 
+##  Use of this source code is governed by a BSD-style license
 ##  that can be found in the LICENSE file in the root of the source
 ##  tree. An additional intellectual property rights grant can be found
-##  in the file PATENTS.  All contributing project authors may 
+##  in the file PATENTS.  All contributing project authors may
 ##  be found in the AUTHORS file in the root of the source tree.
 ##