remove mut

src/client.rs

@@ -84,7 +84,7 @@ impl Client {
     ///
     /// Note that the requests need to have valid IDs, so it is advised to create the requests
     /// with [`Client::build_request`].
-    pub fn send_batch(&mut self, requests: &[Request]) -> Result<Vec<Option<Response>>, Error> {
+    pub fn send_batch(&self, requests: &[Request]) -> Result<Vec<Option<Response>>, Error> {
         if requests.is_empty() {
             return Err(Error::EmptyBatch);
         }