.gitattributes: prevent all magic line ending changes

Fixes #9281

Change-Id: Id060e9cbad086c994ec74b240f5c61e971e5690b
Reviewed-on: https://go-review.googlesource.com/1490Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

.gitattributes

-# see golang.org/issue/9281
-* eol=lf
+# Treat all files in the Go repo as binary, with no git magic updating
+# line endings. Windows users contributing to Go will need to use a
+# modern version of git and editors capable of LF line endings.
+#
+# We'll prevent accidental CRLF line endings from entering the repo
+# via the git-review gofmt checks.
+#
+# See golang.org/issue/9281
+
+* -text