[gtkmm-documentation] Use glibmm-2.60 instead of glibmm-2.58

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 951ed85e2db3631c915ae964efdf6a923d123047
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Nov 8 18:34:32 2018 +0100

    Use glibmm-2.60 instead of glibmm-2.58
    
    We have changed the ABI name in glibmm.

 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/configure.ac b/configure.ac
index 333e0c4..b29f1dd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,7 +25,7 @@ MM_AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 AC_PATH_PROG([PERL], [perl], [perl])
 AC_PROG_SED
 
-PKG_CHECK_MODULES([GIOMM], [giomm-2.58 >= 2.57.1])
+PKG_CHECK_MODULES([GIOMM], [giomm-2.60 >= 2.59.1])
 PKG_CHECK_MODULES([GTKMM], [gtkmm-4.0  >= 3.93.0])
 MM_PKG_CONFIG_SUBST([GTHREAD_CFLAGS], [--cflags-only-other gthread-2.0])