elliptic-curve: bump digest requirement to v0.11

Release PR: #2300

Author: tarcieri

elliptic-curve/Cargo.toml

@@ -26,7 +26,7 @@ subtle = { version = "2.6", default-features = false }
 zeroize = { version = "1.7", default-features = false }
 
 # optional dependencies
-digest = { version = "0.11.0-rc.11", optional = true }
+digest = { version = "0.11", optional = true }
 ff = { version = "0.14.0-rc.0", package = "rustcrypto-ff", optional = true, default-features = false }
 group = { version = "0.14.0-rc.0", package = "rustcrypto-group", optional = true, default-features = false }
 hkdf = { version = "0.13.0-rc.5", optional = true, default-features = false }