Add Numpy 1.18 to Travis builds
Add Numpy 1.18 to Travis builds

tacaswell/scikit-xray,scikit-xray/scikit-xray,Nikea/scikit-xray,tacaswell/scikit-xray,Nikea/scikit-xray,tacaswell/scikit-beam,tacaswell/scikit-xray,tacaswell/scikit-beam,scikit-xray/scikit-xray,Nikea/scikit-xray,tacaswell/scikit-beam,scikit-xray/scikit-xray