cmd/guru: emacs: update default-directory

That way, running guru on /a/foo.go, followed by /b/bar.go won't leave
the user with a display buffer that still defaults to /a/

Change-Id: I3f9b085c6d206ac2adc269fc2009799c624c371a
Reviewed-on: https://go-review.googlesource.com/20475
Reviewed-by: Alan Donovan <adonovan@google.com>
1 file changed