Enable development version of website

[peterdesmet]

Done in 45f07f0 but to be tested

[peterdesmet]

Answer from @maelle on Slack on whether this is supported on docs.ropensci.org:

No, it is not supported at the moment, sorry.

[peterdesmet]

Config reverted in 725788b

[maelle]

Cc @jeroen for info