Bump to GMT 6.2.0

[weiji14]

🎉 GMT 6.2.0 has been released (https://github.com/GenericMappingTools/gmt/releases/tag/6.2.0) on 6 June 2021! It is installable from the conda-forge channel using the following command:

conda install -c conda-forge gmt=6.2.0

TODO:

• Bump the minimum required GMT version to 6.2.0 (Bump the minimum required GMT version to 6.2.0 #1321, @weiji14)
• Fix failing tests (recommend opening 2 PRs, one for rose and one for the others).
  • test_colorbar (1), test_inset (2), test_legend (1), test_logo (1) (Update colorbar, inset, legend and logo baseline images for GMT 6.2.0 #1322, @weiji14)
  • test_plot3d (1) (only broken on Windows, see Update colorbar, inset, legend and logo baseline images for GMT 6.2.0 #1322 (comment))
  • test_rose (5, Some rose tests are wrong #1315, Fix rose tests for GMT 6.2.0 #1324, @michaelgrund)
• Remove xfail pytest markers on tests that are now xpass
  • grdtrack (grdtrack produces incorrect results for xarray.DataArray grid #1309, Remove xfail on grdtrack tests for GMT 6.2.0 #1304, @seisman)
  • makecpt (Remove xfail on makecpt tests for GMT 6.2.0 #1323 @seisman)

Supersedes #1289

Are you willing to help implement and maintain this feature? Yes