all: make copyright headers consistent with one space after period

Continuation of CL 20111.

Change-Id: Ie2f62237e6ec316989c021de9b267cc9d6ee6676
Reviewed-on: https://go-review.googlesource.com/32830
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/bytes/bytes_amd64.go b/src/bytes/bytes_amd64.go
index 9a4e5e3..6affff6 100644
--- a/src/bytes/bytes_amd64.go
+++ b/src/bytes/bytes_amd64.go
@@ -1,4 +1,4 @@
-// Copyright 2016 The Go Authors.  All rights reserved.
+// Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.