Install sdf/1.8 to versioned path

Fixes a mistake from merging forward in #808.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

sdf/1.8/CMakeLists.txt

@@ -82,5 +82,5 @@ add_custom_target(schema1_8 ALL DEPENDS ${SDF_SCHEMA})
 
 set_source_files_properties(${SDF_SCHEMA} PROPERTIES GENERATED TRUE)
 
-install(FILES 1_7.convert ${sdfs} DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/sdformat${SDF_MAJOR_VERSION}/1.8)
-install(FILES ${SDF_SCHEMA} DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/sdformat${SDF_MAJOR_VERSION}/1.8)
+install(FILES 1_7.convert ${sdfs} DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/sdformat${PROJECT_VERSION_MAJOR}/1.8)
+install(FILES ${SDF_SCHEMA} DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/sdformat${PROJECT_VERSION_MAJOR}/1.8)