clippy: fix ref_binding_to_reference lint

Author: apoelstra

src/encode.rs

@@ -76,7 +76,7 @@ impl fmt::Display for Error {
                 "oversized vector allocation: requested {}, maximum {}",
                 r, m
             ),
-            Error::ParseFailed(ref e) => write!(f, "parse failed: {}", e),
+            Error::ParseFailed(e) => write!(f, "parse failed: {}", e),
             Error::UnexpectedEOF => write!(f, "unexpected EOF"),
             Error::InvalidConfidentialPrefix(p) => {
                 write!(f, "invalid confidential prefix: 0x{:02x}", p)