[gnome-documents] build: Use better syntax highlighting in Emacs

[Debarshi Ray <debarshir src gnome org>]

commit 3e203e72f1d73632404488ac13413006d0e8b05f
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu Aug 17 12:55:13 2017 +0200

    build: Use better syntax highlighting in Emacs
    
    The Autoconf mode gives better syntax highlighting in Emacs than the
    M4 mode.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786418

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 857b31d..fde9705 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-dnl -*- mode: m4 -*-
+dnl -*- mode: Autoconf -*-
 AC_PREREQ(2.63)
 AC_INIT([gnome-documents],[3.25.90],[],[gnome-documents])