fix(json): bump serde_json dependency and fix failing test

src/response.rs

@@ -533,16 +533,13 @@ impl Response {
     #[cfg(feature = "json")]
     pub fn into_json<T: DeserializeOwned>(self) -> io::Result<T> {
         use crate::stream::io_err_timeout;
-        use std::error::Error;
 
         let reader = self.into_reader();
         serde_json::from_reader(reader).map_err(|e| {
             // This is to unify TimedOut io::Error in the API.
-            // We make a clone of the original error since serde_json::Error doesn't
-            // let us get the wrapped error instance back.
-            if let Some(ioe) = e.source().and_then(|s| s.downcast_ref::<io::Error>()) {
-                if ioe.kind() == io::ErrorKind::TimedOut {
-                    return io_err_timeout(ioe.to_string());
+            if let Some(kind) = e.io_error_kind() {
+                if kind == io::ErrorKind::TimedOut {
+                    return io_err_timeout(e.to_string());
                 }
             }