Patch script does not work with BSD sed

[fxcoudert]

On macOS, or another BSD system, patching does not succeed:

$ ./patch_lammps.sh $HOME/lammps
Copying files...
Updating CMakeLists.txt...
sed: 1: "/Users/fx/lammps/cmake/ ...": invalid command code f
Done!

Note the sed error, that's because BSD sed expects an argument after -i:

NAME
     sed – stream editor

SYNOPSIS
     sed [-Ealnru] command [-I extension] [-i extension] [file ...]
     sed [-Ealnru] [-e command] [-f command_file] [-I extension] [-i extension] [file ...]

Specifying a suffix is the only way to make the command work for both BSD and GNU sed.

# Update CMakeLists.txt
sed -i.bak "s/set(CMAKE_CXX_STANDARD 11)/set(CMAKE_CXX_STANDARD 14)/" $lammps_dir/cmake/CMakeLists.txt