Fix Github Pages deployment from Travis (#410)
Fix Github Pages deployment from Travis (#410)

Revert some aspects of #404 as the `cleanup` tag isn't actually supported yet according to https://github.com/fatiando/verde/pull/250. Also explicitly specifying the build to be on Linux - Ubuntu Bionic 18.04.
GenericMappingTools/gmt-python,GenericMappingTools/gmt-python