Change LitIntUnsuffixed to LitInt to reflect rustc  

Fix the nightly which breaks with 

```
vertex_format.rs:148:31: 148:52 error: unresolved name `ast::LitIntUnsuffixed`.
vertex_format.rs:148             cx.expr_lit(span, ast::LitIntUnsuffixed(1)),
```

Change: https://github.com/rust-lang/rust/commit/0dc215741b34236c310e409c437600ba0165c97c