scripts/functions: use portable 'gzip -dc'
'zcat' on MacOS-X is broken (it is not gzip's zcat, but compres' zcat).
Use 'gzip -dc' for portability, as suggested by Anthony.
Reported-by: Fernando Ortiz <fortiz2k@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Anthony Foiani <anthony.foiani@gmail.com>