Update version for v3.0.0-rc4 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/VERSION b/VERSION
index 9613415..e04ef0c 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.12.93
+2.12.94