configure.ac: Bump git master version to 1.0.90

We use 1.0.90 as the version number for the git master code.  This way it's
always newer than any stable version.
diff --git a/configure.ac b/configure.ac
index f9075ae..1ba467b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,6 @@
 AC_PREREQ([2.64])
 AC_INIT([weston],
-        [1.0.0],
+        [1.0.90],
         [https://bugs.freedesktop.org/enter_bug.cgi?product=weston],
         [weston],
         [http://wayland.freedesktop.org/])