configure.ac: bump version to 2.4.40 for release
diff --git a/configure.ac b/configure.ac
index 8c28107..0c19929 100644
--- a/configure.ac
+++ b/configure.ac
@@ -20,7 +20,7 @@
 
 AC_PREREQ([2.63])
 AC_INIT([libdrm],
-        [2.4.39],
+        [2.4.40],
         [https://bugs.freedesktop.org/enter_bug.cgi?product=DRI],
         [libdrm])