Docs 7.3.3 Constraints: incorrect example code 

The given example:

```
pure fn is_less_than(int a, int b) -> bool {
     ret a < b;
}
```

Should be:

```
pure fn is_less_than(a: int, b: int) -> bool {
     ret a < b;
}
```

(Changes to the argument list)

Patch to follow
