configure.ac: Bump configure.ac version to 1.2.90
We usually do this when we branch off the stable branch, better late than
never.
diff --git a/configure.ac b/configure.ac
index 156237f..802c208 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,6 @@
m4_define([weston_major_version], [1])
m4_define([weston_minor_version], [2])
-m4_define([weston_micro_version], [0])
+m4_define([weston_micro_version], [90])
m4_define([weston_version],
[weston_major_version.weston_minor_version.weston_micro_version])