Make all package.xml files consistently use format 3. (#405)

nav2_amcl/package.xml

 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
   <name>nav2_amcl</name>
   <version>0.1.1</version>
   <description>

nav2_costmap_2d/package.xml

 <?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>nav2_costmap_2d</name>
   <version>0.1.1</version>

nav2_dwb_controller/dwb_controller/package.xml

 <?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>dwb_controller</name>
   <version>0.1.1</version>

nav2_dwb_controller/nav2_dwb_controller/package.xml

 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
   <name>nav2_dwb_controller</name>
   <version>0.1.1</version>
   <description>

nav2_dwb_controller/nav_2d_utils/package.xml

 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
   <name>nav_2d_utils</name>
   <version>0.1.1</version>
   <description>A handful of useful utility functions for nav_2d packages.</description>

nav2_map_server/package.xml

 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
   <name>nav2_map_server</name>
   <version>0.1.1</version>
   <description>

nav2_voxel_grid/package.xml

 <?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>nav2_voxel_grid</name>
   <version>0.1.1</version>

navigation2/package.xml

 <?xml version="1.0"?>
-<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
   <name>navigation2</name>
   <version>0.1.1</version>
   <description>
@@ -29,7 +29,7 @@
   <exec_depend>nav2_tasks</exec_depend>
   <exec_depend>nav2_util</exec_depend>
   <exec_depend>nav2_voxel_grid</exec_depend>
-  
+
   <export>
     <metapackage/>
   </export>