Rustdoc: source links are missing

[RalfJung]

The latest nightly version of the standard library docs does not seem to have source links any more:

https://doc.rust-lang.org/nightly/std/any/struct.TypeId.html#method.of
vs
https://doc.rust-lang.org/beta/std/any/struct.TypeId.html#method.of

I hope that's some kind of accident, I use these source links all the time to figure out where stuff is implemented. :)

[fmease]

Yea, we've been talking on Zulip: https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/source.20links.20missing.20for.20nightly.20std.20docs/near/563724274. Unfortunately GG couldn't repro it locally, so we're still searching. We have a bisection and possibly a fix: #149919.