fix package.xml and add myself as maintainer

package.xml

@@ -1,19 +1,20 @@
 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
 <package format="3">
   <name>apriltag</name>
   <version>3.3.0</version>
   <description>AprilTag detector library</description>
 
   <maintainer email="[email protected]">Max Krogius</maintainer>
   <maintainer email="[email protected]">Wolfgang Merkt</maintainer>
-
-  <author email="[email protected]">Edwin Olson</author>
-  <author email="[email protected]">Max Krogius</author>
+  <maintainer email="[email protected]">Christian Rauch</maintainer>
 
   <license>BSD</license>
   <url>https://april.eecs.umich.edu/software/apriltag.html</url>
 
+  <author email="[email protected]">Edwin Olson</author>
+  <author email="[email protected]">Max Krogius</author>
+
   <buildtool_depend>cmake</buildtool_depend>
   <build_depend condition="$ROS_PYTHON_VERSION == 3">python3-numpy</build_depend>