Fix doc warnings during CI?

[briochemc]

This is a docs PR. It essentially does 2 things:

• bumps documenter version
• lets GR know there is no screen output via an environment variable (see https://discourse.julialang.org/t/generation-of-documentation-fails-qt-qpa-xcb-could-not-connect-to-display/60988), which removes many of the display warnings ~and speeds up the docs build significantly~ [EDIT: not sure about that one]

[briochemc]

It seems this PR solves whatever the current issue is with the CI build of the documentation (see, e.g., PR #61).

Once this is merged (after @jw3126 or @gustaphe approves), I'll rebase #61 so we can get the docs deployed on the PR branch.

[gustaphe]

I'm not sure I understand what it does, but if it builds I have no objections.

[briochemc]

I'm not sure I understand what it does, but if it builds I have no objections.

I’m not entirely sure (I merely copied the line from Documenter’s docs) but AFAIU, when deploying the docs, Plots (Or rather the GR backend) tries to show the output on some GKS “workstation type“, which this line apparently specifies as a special, no-output type.

[briochemc]

Less warnings sounds good :)

Well it's more than that actually... As you can see here, I retriggered a past Documentation job that worked last month, and this time it failed just like PR #61. So I think we need this fix now.

[briochemc]

And to reassure you and save you a few clicks, this is what the current Documenter docs shows:

[jw3126]

Thanks a lot @briochemc

[briochemc]

I merged this and we can always revert it back if I did something wrong (it only impacts how the docs are built, not the package itself really)!