Fix include install directory (#50)

Author: paulbovbel

CMakeLists.txt

@@ -62,7 +62,7 @@ install(EXPORT ${PROJECT_NAME}_Targets
 install(FILES "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
               "${PROJECT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
         DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/${PROJECT_NAME}/cmake)
-install(DIRECTORY ${PROJECT_SOURCE_DIR}/include DESTINATION include)
+install(DIRECTORY ${PROJECT_SOURCE_DIR}/include/ DESTINATION include)
 
 if(ENABLE_TESTS)
   # The test targets