fix CONTRIBUTING
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a10a3cf..26b2915 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,6 +1,6 @@
 This service is composed of 3 parts.
 
-1. The mojo definition, [gcm.mojom].
+1. The mojo definition, [gcm.mojom](gcm.mojom).
 2. The Dart bindings, located in `packages/gcm/`.
 3. The Flutter mojo service, located in `src/`.