bumping humble to 2.3.1 for release

Signed-off-by: Steve Macenski <stevenmacenski@gmail.com>

Author: SteveMacenski

��package.xml

@@ -2,7 +2,7 @@
 <?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
 <package format ="3">
     <name>nonpersistent_voxel_layer</name>
-    <version>2.4.0</version>
+    <version>2.3.1</version>
     <description>include
         This package provides an implementation of a 3D costmap that takes in sensor
         data from the world, builds a 3D occupancy grid of the data for only one iteration.