Bump the version to 0.4.0 to prepare the release

Author: jerryshao

gradle.properties

@@ -9,7 +9,7 @@ org.gradle.caching=true
 org.gradle.jvmargs=-Xmx4g
 
 #version that is going to be updated automatically by releases
-version = 0.4.1-SNAPSHOT
+version = 0.4.0
 
 #sonatype credentials
 SONATYPE_USER = admin