MINOR: Commit .gitattributes

Commit .gitattributes to the repository to allow GitHub downloads to
properly fill in the SUBVERS and VERDATE files. It also prevents the
engineer in charge of the release to forget creating it when a new branch
is released.

see https://www.mail-archive.com/haproxy@formilux.org/msg38107.html

No functional change, may be backported everywhere.
1 file changed