Update libigl.cmake

Former-commit-id: 20c2792aa8a13807755df05c9c69192a80f49f7f

shared/cmake/libigl.cmake

@@ -141,7 +141,7 @@ if(LIBIGL_WITH_CGAL)
     if(WIN32)
       set(Boost_USE_STATIC_LIBS ON) # Favor static Boost libs on Windows
     endif()
-	target_include_directories(igl_cgal ${IGL_SCOPE} "${GMP_INCLUDE_DIR}" "${MPFR_INCLUDE_DIR}")
+    target_include_directories(igl_cgal ${IGL_SCOPE} "${GMP_INCLUDE_DIR}" "${MPFR_INCLUDE_DIR}")
     find_package(Boost 1.48 REQUIRED thread system)
     target_include_directories(igl_cgal ${IGL_SCOPE} ${CGAL_INCLUDE_DIRS} ${Boost_INCLUDE_DIRS})
     target_link_libraries(igl_cgal ${IGL_SCOPE} CGAL::CGAL CGAL::CGAL_Core ${Boost_LIBRARIES})