Update dev release to 6.0.0rc4

[seisman]

Checklist

• Used a fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

@conda-forge-admin, please rerender

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[seisman]

@conda-forge-admin, please rerender

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[seisman]

@conda-forge-admin, please rerender

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[seisman]

@conda-forge-admin, please rerender

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you but ran into some issues, please ping conda-forge/core for further assistance.

[seisman]

@ocefpaf @leouieda This PR is ready for review.

This PR updates to 6.0.0rc4 in the devel channel. As GMT fails to run with paths longer than 256 characters, e.g. /home/conda/feedstock_root/build_artifacts/gmt_1567804993613/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_pl, thus I have to apply two patches to the 6.0.0rc4 tarballs. The same patches are already merged into the GMT latest source codes.

[seisman]

@leouieda @ocefpaf Can any of you review this PR?