Update version for v2.3.0 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/VERSION b/VERSION
index c3c2c0e..276cbf9 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.2.94
+2.3.0