[gtkmm] Use libsigc++-3.0.tag for libsigc++ documentation

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 710c0ed37ca90bc28148886f962e26449f27d322
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Apr 26 16:36:09 2018 +0200

    Use libsigc++-3.0.tag for libsigc++ documentation

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index f144965..7d7a92d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -124,7 +124,7 @@ MM_ARG_DISABLE_DEPRECATED_API([GDKMM GTKMM])
 
 MM_ARG_ENABLE_DOCUMENTATION
 MM_ARG_WITH_TAGFILE_DOC([libstdc++.tag], [mm-common-libstdc++])
-MM_ARG_WITH_TAGFILE_DOC([libsigc++-2.0.tag], [sigc++-2.0])
+MM_ARG_WITH_TAGFILE_DOC([libsigc++-3.0.tag], [sigc++-3.0])
 MM_ARG_WITH_TAGFILE_DOC([glibmm-2.58.tag], [glibmm-2.58])
 MM_ARG_WITH_TAGFILE_DOC([cairomm-1.16.tag], [cairomm-1.16])
 MM_ARG_WITH_TAGFILE_DOC([pangomm-2.42.tag], [pangomm-2.42])