fixup! Addign missing word

Author: NunoAlexandre

DEVELOPING.md

@@ -95,7 +95,7 @@ End-to-end tests that run against a real node are implemented in
 `client/tests/end_to_end.rs`.
 
 To run specific tests sequentially as opposed to the parallel default,
-we use the [serial-test](https://crates.io/crates/serial_test), simply
+we use the [serial-test](https://crates.io/crates/serial_test) crate, simply
 having to mark the targeted tests with `#[serial]`.