API docs: link previews do not work on root pages

Created by: slimsag

no link preview (under root /-/docs):

https://sourcegraph.com/github.com/exoscale/egoscale/-/docs?CreateAffinityGroup.AsyncResponse

link preview (under sub-path of /-/docs/v2):

https://sourcegraph.com/github.com/exoscale/egoscale/-/docs/v2?ElasticIP