Improve error message

Author: Heliozoa

crates/tmc-testmycode-client/src/client.rs

@@ -130,7 +130,7 @@ impl TestMyCodeClient {
             .0
             .root_url
             .join("/oauth/token")
-            .map_err(|e| TestMyCodeClientError::UrlParse("oauth/token".to_string(), e))?;
+            .map_err(|e| TestMyCodeClientError::UrlParse(self.0.root_url.to_string() + "/oauth/token", e))?;
 
         let credentials = api_v8::get_credentials(self, client_name)?;