Rename msgs to msg (BehaviorTree#81)

Fixes the issue rosidl_adapter.parser.InvalidResourceName
when calling ros2 interface show btcpp_ros2_interfaces *

Author: AdrianZw

btcpp_ros2_interfaces/CMakeLists.txt

@@ -8,7 +8,7 @@ find_package(ament_cmake REQUIRED)
 find_package(rosidl_default_generators REQUIRED)
 
 rosidl_generate_interfaces(btcpp_ros2_interfaces
-    "msgs/NodeStatus.msg"
+    "msg/NodeStatus.msg"
     "action/ExecuteTree.action"
     "action/Sleep.action")