ecdsa: work around nightly-2020-10-06 breakage

The `ecdsa` crate no longer builds on `nightly`, possibly due to:

rust-lang/rust#77638

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

This commit works around the issue.

ecdsa/src/sign.rs

@@ -87,7 +87,7 @@ where
         AffinePoint<C>: Clone + Debug,
     {
         VerifyKey {
-            public_key: (C::ProjectivePoint::generator() * &self.secret_scalar).to_affine(),
+            public_key: (C::ProjectivePoint::generator() * *self.secret_scalar).to_affine(),
         }
     }