Travis: update to a newer xcode image
Travis: update to a newer xcode image

Hopefully, this will bring in a newer version of Java?
1.8.0_91 is too old; we need at least 1.8.0_101.

kephale/ThreeDViewer,scenerygraphics/SciView,kephale/ThreeDViewer,scenerygraphics/SciView