No trailing comma changes in debug_assert calls

`rustfmt` does not change trailing commas in `debug_assert` invocations, and both of the following are left unchanged:

```rust
debug_assert(a == b,);
debug_assert(a == b);
```

While obviously macros should be handled with care, `rustfmt` should be able to handle at least *common* function-like ones as if they were functions, I think.