Bump version to v0.4

Change-Id: I50c63ff8219a6982e0bbc34a939ce274dbacf976
diff --git a/Changes b/Changes
index 3d045db..4c001ca 100644
--- a/Changes
+++ b/Changes
@@ -1,4 +1,4 @@
-0.3.900 unreleased
+0.4 2021-07-29
         - korapxml2conllu option -e <regex> added to extract element/attributes to comments
 
 0.3 2021-02-15