Now both
./install prod --ignore-root-warning
./install --ignore-root-warning prod
will work
$1 was both used for the environment and the root flag
Fixeswallabag/wallabag#3884
* Move `Makefile` to `GNUmakefile`, which GNU `make` picks first
* Add `Makefile` so other `make`s forward to `gmake`
* Set the `SHELL` variable and let `make` handle the shell
Signed-off-by: Olivier Mehani <shtrom@ssji.net>