Fixed example showing old API (Blazored#192)

README.md

@@ -143,7 +143,7 @@ In order to show a toast you have to inject the `IToastService` into the compone
 To show a toast just click one of the buttons below.
 
 <button class="btn btn-info" @onclick="@(() => toastService.ShowInfo("I'm an INFO message"))">Info Toast</button>
-<button class="btn btn-success" @onclick="@(() => toastService.ShowSuccess("I'm a SUCCESS message with a custom title", "Congratulations!"))">Success Toast</button>
+<button class="btn btn-success" @onclick="@(() => toastService.ShowSuccess("I'm a SUCCESS message with a custom title"))">Success Toast</button>
 <button class="btn btn-warning" @onclick="@(() => toastService.ShowWarning("I'm a WARNING message"))">Warning Toast</button>
 <button class="btn btn-danger" @onclick="@(() => toastService.ShowError("I'm an ERROR message"))">Error Toast</button>
 ```