Fix a typo s/training/trailing/ in ProtoRPC.h
diff --git a/src/objective-c/ProtoRPC/ProtoRPC.h b/src/objective-c/ProtoRPC/ProtoRPC.h
index 0fd53bf..25f0253 100644
--- a/src/objective-c/ProtoRPC/ProtoRPC.h
+++ b/src/objective-c/ProtoRPC/ProtoRPC.h
@@ -54,7 +54,7 @@
/**
* Issued when a call finished. If the call finished successfully, \p error is nil and \p
- * trainingMetadata consists any trailing metadata received from the server. Otherwise, \p error
+ * trailingMetadata consists any trailing metadata received from the server. Otherwise, \p error
* is non-nil and contains the corresponding error information, including gRPC error codes and
* error descriptions.
*/