Try to fix travis installation of gcc-8 on xenial.
Try to fix travis installation of gcc-8 on xenial.

scoder/cython,da-woods/cython,cython/cython,cython/cython,scoder/cython,da-woods/cython,cython/cython,scoder/cython,scoder/cython,cython/cython,da-woods/cython,da-woods/cython