Fix expression in script

[vondele]

thanks for working on the external engine functionality. I believe this will be a great feature.

Testing the current setup, I found this error message

$ ./stockfish quit
./stockfish: 10: [[: not found
Stockfish 15 by the Stockfish developers (see AUTHORS file)

which probably is kind of syntax error. I fixed it locally as shown here, tests fine (and finds the right arch).

$ ./stockfish quit
Stockfish 15 by the Stockfish developers (see AUTHORS file)

I'm not sure this is the cleanest solution, however.

[niklasf]

Thanks! Looks like this was using a bash feature, which doesn't work if #!/bin/sh is not bash.