Bump version to v0.4.0

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>
diff --git a/VERSION.txt b/VERSION.txt
index 268b033..fb7a04c 100644
--- a/VERSION.txt
+++ b/VERSION.txt
@@ -1 +1 @@
-v0.3.0
+v0.4.0