Bump the required minimum GMT version to 6.1.1

[weiji14]

Description of proposed changes

Bumps gmt from 6.1.0 to 6.1.1.

• Release notes
• Commits

TODO:

• Bump the required minimum GMT version to 6.1.1
• Remove pytest xfails that were set to previous 6.1.0 version
• Remove compatibility codes for GMT 6.1.0 (if any)
• etc

Issues marked upstream that are resolved in GMT 6.1.1 will be handled in separate Pull Requests.

Supersedes #507

Fixes #

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

[seisman]

There are some tests marked as "xfail".

pygmt/pygmt/tests/test_clib.py

Lines 405 to 408 in fc246e7

	@pytest.mark.xfail(
	condition=gmt_version < Version("6.1.1"),
	reason="GMT_Put_Strings only works for GMT 6.1.1 and above",
	)

Remove these "xfail" markers?

Also update this one:

pygmt/pygmt/tests/test_clib.py

Line 691 in fc246e7

assert Version(lib.get_default("API_VERSION")) >= Version("6.1.0")

[weiji14]

Good catch, thanks @seisman! Let me know if you find any other loose ends, I feel like there's a lot of them lying around.