Remove xfail on grdtrack tests for GMT 6.2.0 (#1304)
Remove xfail on grdtrack tests for GMT 6.2.0 (#1304)

* Remove xfail on grdtrack tests for GMT 6.2.0
* Update the grdtrack tests so that it pass for GMT 6.2.0
GenericMappingTools/gmt-python,GenericMappingTools/gmt-python