bump deps, fix clippy warnings

src/request.rs

@@ -132,7 +132,7 @@ impl Request {
     /// ```
     #[cfg(feature = "json")]
     pub fn send_json(&mut self, data: SerdeValue) -> Response {
-        if let None = self.header("Content-Type") {
+        if self.header("Content-Type").is_none() {
             self.set("Content-Type", "application/json");
         }
         self.do_call(Payload::JSON(data))