bumping to 2.2.0 for galactic release (#219)

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>spatio_temporal_voxel_layer</name>
-  <version>2.1.3</version>
+  <version>2.2.0</version>
   <description>The spatio-temporal 3D obstacle costmap package</description>
 
   <maintainer email="stevenmacenski@gmail.com">Steve Macenski</maintainer>