Update version for v2.6.0-rc4 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/VERSION b/VERSION
index 127ee42..7ff039e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.5.93
+2.5.94