mktemp not working on BusyBox

[CaptainQuirk]

Hi !

I'm using a custom docker image based on bats image on which I have installed bats-file. The version of mktemp included in the bats docker image is not the same as the one expected in bats-file.

In fact, the long options --directory and --tmp-dir, althoug more legible, are not available.

We should use the -d and -p short options respectively