ros-install-parallel-cmake.md

From https://answers.ros.org/question/293119/how-can-i-updateremove-cmake-without-partially-deleting-my-ros-distribution/

cd ~/Downloads/cmake-3.12.0-rc3/   # or wherever you downloaded cmake
./bootstrap --prefix=$HOME/cmake-install
make 
make install
export PATH=$HOME/cmake-install/bin:$PATH
export CMAKE_PREFIX_PATH=$HOME/cmake-install:$CMAKE_PREFIX_PATH