PATH setting in BATS tests/helpers/command.bash is not correct on Windows

[jandubois]

We use this code

docker_exe() {
    # Add path to bundled credential helpers to the front of the PATH
    PATH="$PATH_RESOURCES/$PLATFORM/bin:$PATH" "$PATH_RESOURCES/$PLATFORM/bin/docker$EXE" "$@" | no_cr
}

To update the PATH before running docker$EXE, but if we are running the Windows executable, then this will have no effect.

Similar code now also exists for the spin function.