Fix cmake abosule paths in build interface (#331)

Author: Saurav Agarwal

CMakeLists.txt

@@ -51,7 +51,7 @@ endif()
 set_target_properties(${PROJECT_NAME} PROPERTIES EXPORT_NAME TorchSparse)
 
 target_include_directories(${PROJECT_NAME} INTERFACE
-  $<BUILD_INTERFACE:${HEADERS}>
+  "$<BUILD_INTERFACE:${HEADERS}>"
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
 include(GNUInstallDirs)