[vte] build: vala: Bump vapigen required version to 0.24

[Christian Persch <chpe src gnome org>]

commit c153782c0654f9e99a77207b217fb2778397972e
Author: Christian Persch <chpe src gnome org>
Date:   Wed Apr 26 11:13:22 2017 +0200

    build: vala: Bump vapigen required version to 0.24
    
    https://bugzilla.gnome.org/show_bug.cgi?id=781322

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 9ec2dc9..5fe80dc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -378,7 +378,7 @@ if test -z "$enable_vala"; then
 fi
 
 m4_ifdef([VAPIGEN_CHECK],
-  [VAPIGEN_CHECK([0.18])],
+  [VAPIGEN_CHECK([0.24])],
   [if test "$enable_vala" = "yes"; then
      AC_MSG_ERROR([[Vala requested but M4 macros not installed. Try --disable-vala]])
    fi