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

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>