Use current stable version of JCPI

Hey Bill

Nice to see you coding again on your chess engine! I have noticed that you switched to the latest version of JCPI. I hope the transition and refactoring wasn't that painful. :)

To have you not going through it again, I've created this pull request to change the version to the stable branch. The branch 1.2.x might probably change a lot, that's why it's currently tagged as alpha. Please consider merging this in, so that you're building against the stable version.

Cheers,
Poky