[gtk+] Update Makefile.am for one more gitignore rule

[Jasper St. Pierre <jstpierre src gnome org>]

commit a0337f97556002c9b9bad122ea6ef48d9ef10e67
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Thu Jun 19 11:13:17 2014 -0400

    Update Makefile.am for one more gitignore rule

 Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 40471d1..cda16ce 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -24,6 +24,7 @@ MAINTAINERCLEANFILES = \
        $(GITIGNORE_MAINTAINERCLEANFILES_TOPLEVEL) \
        $(GITIGNORE_MAINTAINERCLEANFILES_M4_LIBTOOL) \
        $(GITIGNORE_MAINTAINERCLEANFILES_MAKEFILE_IN) \
+       $(srcdir)/m4/gtk-doc.m4 \
        $(srcdir)/INSTALL \
        $(srcdir)/README \
        $(srcdir)/omf.make \