[hotfix][release] Update version to 3.4.0.

Author: lvyanquan

pom.xml

@@ -59,7 +59,7 @@ limitations under the License.
     </scm>
 
     <properties>
-        <revision>3.4-SNAPSHOT</revision>
+        <revision>3.4.0</revision>
         <scala.binary.version>2.12</scala.binary.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <!-- Enforce single fork execution due to heavy mini cluster use in the tests -->