docs: update broken link to nightly branch

- changed the link from `main` to `nightly` for the operators example

docs/manual/operators.mdx

@@ -1030,7 +1030,7 @@ operations like printing complex values. We'll also allow mixing `Complex` and
 
 This example builds our `Complex` struct incrementally. You can also find the
 [complete example in the public Mojo GitHub
-repo](https://github.com/modularml/mojo/tree/main/examples/operators).
+repo](https://github.com/modularml/mojo/tree/nightly/examples/operators).
 
 :::note