type/literals/input.md: fixing 404 link to modules page

Currently, the link to the `modules` page within `examples/type/literals/input.md` leads to a 404 error on `http://rustbyexample.com/modules.html`. 

Fixed by changing `http://rustbyexample.com/modules.html` -> `http://rustbyexample.com/mod.html`.

UPDATE: Fixed `make test` errors as reported in [issue #230](https://github.com/japaric/rust-by-example/issues/230). There are still some unfixed test errors though.