updated the path to fix compilation error

[ssahai]

Fixing the following error:

error: couldn't read src/range_proof/../docs/range-proof-protocol.md: No such file or directory (os error 2)
--> src/range_proof/mod.rs:2:18
|
2 | #![doc(include = "../docs/range-proof-protocol.md")]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ couldn't read file

[hdevalence]

Hey, thanks for sending this PR!

I'm going to close it, though, because it's a duplicate of #283 -- the only reason that one hasn't been merged yet is that this change to import path roots for doc(include) happened recently, and we need to check which nightly version so that we can update the CI pin (#287) so the CI isn't out of sync, and that required fixing up #277 because the development branch got out of sync.

Thanks for your understanding :)