all: single space after period

Follow CL 20022 and consistently use single space after a period in
documentation.

Generated with:

$ perl -i -npe 's,^(\s*// .+[a-z]\.)  +([A-Z]),$1 $2,' $(git grep -l -E '^\s*//(.+\.)  +([A-Z])')

Change-Id: Ia29ad823668f060e81293e848a79fc4b4857d94b
Reviewed-on: https://go-review.googlesource.com/73530
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/unix/pagesize_unix.go b/unix/pagesize_unix.go
index 45afcf7..83c85e0 100644
--- a/unix/pagesize_unix.go
+++ b/unix/pagesize_unix.go
@@ -1,4 +1,4 @@
-// Copyright 2017 The Go Authors.  All rights reserved.
+// Copyright 2017 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.