elliptic-curve: work around nightly-2020-10-06 breakage (#328)

The `elliptic-curve` crate no longer builds on `nightly`.

Possible cause:

rust-lang/rust#77638

Unfortunately this means rustdoc builds on https://docs.rs fail!

This commit works around the issue.

elliptic-curve/src/ecdh.rs

@@ -73,7 +73,8 @@ where
     ///
     /// The `compress` flag enables point compression.
     pub fn public_key(&self) -> PublicKey<C> {
-        (C::ProjectivePoint::generator() * &self.scalar)
+        #[allow(clippy::op_ref)]
+        (C::ProjectivePoint::generator() * &*self.scalar)
             .to_affine()
             .into()
     }