Update version number on front page

Author: Erik Svedang

README.md

@@ -9,7 +9,7 @@
 
 <i>WARNING! This is a research project and a lot of information here might become outdated and misleading without any explanation. Don't use it for anything important just yet!</i>
 
-<i>[Version 0.3.0](https://github.com/carp-lang/Carp/releases/tag/v0.3.0) of the language is out!</i>
+<i>[Version 0.4.0 of the language is out!](https://github.com/carp-lang/Carp/releases/)</i>
 
 ## About