git tag error in CmakeLists.txt

[clarobit]

from https://github.com/pyk/cmake-tutorial#using-cmake-with-3rd-party-library

Third-party library

include(ExternalProject)
ExternalProject_Add(googletest
PREFIX "${CMAKE_BINARY_DIR}/lib"
GIT_REPOSITORY "https://github.com/google/googletest.git"
GIT_TAG "master" # It should be main not master
CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/lib/installed
)

it's right in file
but wrong in README.md