[CI] build SC 3.10 without X11 or HID

This MR changes the version of SuperCollider that is used by our CI script. We now build 3.10 (currently beta2, release ETA Fall 2018). This allows building SC without X11 (-DNO_X11=ON), which eliminates one package dependency. The HID support was also turned off (-DSC_HIDAPI=OFF) in order to eliminate another dependency.

Also, fixes a typo and adds a comment about installing JACK.