build: fix broken command-list.h generation with core.autocrlf

The script generate-cmdlist.sh needs input text files in UNIX line ending to work correctly. It's been fine even with core.autocrlf set because Documentation/git-*.txt is forced LF conversion. But this leaves out gitk.txt and also Documentation/*config.txt that recently becomes new input for this script. Update the attribute file to force LF on all *.txt files to be on the safe side. For more details, please see 00ddc9d13c (Fix build with core.autocrlf=true - 2017-05-09) Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>