Looks like this was intended to match a literal period to restrict
this to `.go` files, but in POSIX grep, the unescaped period matches
any character.

Change-Id: I20e00323baa9e9631792eff5035966297665bbee
Reviewed-on: https://go-review.googlesource.com/19880Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>