fix typo

cmake/export-cpptools.cmake

@@ -8,7 +8,7 @@ install(TARGETS ${CPP_TOOLS_TARGETS}
 install(EXPORT cpp-tools-targets
         FILE cpp-tools-targets.cmake
         NAMESPACE cpp_tools::
-        DESTINATION lib/cmake/cpp-tools)
+        DESTINATION lib/cmake/cpp_tools)
 
 foreach(target ${CPP_TOOLS_TARGETS})
     install(DIRECTORY ${CPP_TOOLS_ROOT}/${target}/include/cpp_tools/${target}