build-sys: release++

Increment release number to v2.13.1

Signed-off-by: Karel Zak <kzak@redhat.com>
diff --git a/configure.ac b/configure.ac
index d073be1..16c897c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-AC_INIT(util-linux-ng, 2.13, kzak@redhat.com)
+AC_INIT(util-linux-ng, 2.13.1-rc1, kzak@redhat.com)
 
 AC_PREREQ(2.59)