Prepare for 3.4.0 release

DAFFODIL-2740
diff --git a/build.sbt b/build.sbt
index 2da01e7..841d202 100644
--- a/build.sbt
+++ b/build.sbt
@@ -152,7 +152,7 @@
 
 lazy val commonSettings = Seq(
   organization := "org.apache.daffodil",
-  version := "3.4.0-SNAPSHOT",
+  version := "3.4.0",
   scalaVersion := "2.12.17",
   crossScalaVersions := Seq("2.12.17"),
   scalacOptions ++= buildScalacOptions(scalaVersion.value),