Fix spelling (#271)

Author: drewstone

client/beefy/src/keystore.rs

@@ -57,7 +57,7 @@ impl BeefyKeystore {
 
 	/// Sign `message` with the `public` key.
 	///
-	/// Note that `message` usually will be pre-hashed before being singed.
+	/// Note that `message` usually will be pre-hashed before being signed.
 	///
 	/// Return the message signature or an error in case of failure.
 	pub fn sign(&self, public: &Public, message: &[u8]) -> Result<Signature, error::Error> {