Add example_interfaces to desktop repos file (#83)

Needed to build ros2_java_examples

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

Author: jacobperron

ros2_java_desktop.repos

@@ -7,6 +7,10 @@ repositories:
     type: git
     url: https://github.com/ros2/common_interfaces
     version: master
+  ros2/example_interfaces:
+    type: git
+    url: https://github.com/ros2/example_interfaces.git
+    version: master
   ros2/rcl_interfaces:
     type: git
     url: https://github.com/ros2/rcl_interfaces.git