remove deprecated usage of the cause function

Author: Mr-Leshiy

src/codec/http.rs

@@ -228,7 +228,7 @@ impl Display for HttpCodecError {
 }
 
 impl Error for HttpCodecError {
-	fn cause(&self) -> Option<&dyn Error> {
+	fn source(&self) -> Option<&(dyn Error + 'static)> {
 		match *self {
 			HttpCodecError::Io(ref error) => Some(error),
 			HttpCodecError::Http(ref error) => Some(error),

src/result.rs

@@ -92,7 +92,7 @@ impl fmt::Display for WebSocketOtherError {
 }
 
 impl Error for WebSocketOtherError {
-	fn cause(&self) -> Option<&dyn Error> {
+	fn source(&self) -> Option<&(dyn Error + 'static)> {
 		match *self {
 			WebSocketOtherError::HttpError(ref error) => Some(error),
 			WebSocketOtherError::UrlError(ref error) => Some(error),

src/server/upgrade/mod.rs

@@ -217,7 +217,7 @@ impl Display for HyperIntoWsError {
 }
 
 impl Error for HyperIntoWsError {
-	fn cause(&self) -> Option<&dyn Error> {
+	fn source(&self) -> Option<&(dyn Error + 'static)> {
 		match *self {
 			HyperIntoWsError::Io(ref e) => Some(e),
 			HyperIntoWsError::Parsing(ref e) => Some(e),

websocket-base/src/result.rs

@@ -54,12 +54,11 @@ impl fmt::Display for WebSocketError {
 }
 
 impl Error for WebSocketError {
-	#[allow(deprecated)]
-	fn cause(&self) -> Option<&dyn Error> {
+	fn source(&self) -> Option<&(dyn Error + 'static)> {
 		match *self {
 			WebSocketError::IoError(ref error) => Some(error),
 			WebSocketError::Utf8Error(ref error) => Some(error),
-			WebSocketError::Other(ref error) => error.cause(),
+			WebSocketError::Other(ref error) => error.source(),
 			_ => None,
 		}
 	}