Latest documentation build fails to generate manual

[timurgordon]

https://threefoldtech.github.io/web3_proxy/manual is supposed to display the manual for web3proxy.

[despiegk]

see https://github.com/freeflowuniverse/spiderlib/issues/12

[brandonpille]

I fixed the isse in the documentation that resulted in CI failing to generate the docs. But I didn't fix the fact that it silently continues execution when generating the docs failed. We should fix the doc.vsh to make the CI fail when the documentation generation failed. We want to know immediately when the generation of the documentation failed so that we can handle quickly.

[brandonpille]

see freeflowuniverse/spiderlib#12

We are already doing this in the web3_proxy repo.