Head branch renamed to "trunk"

The HEAD branch has been renamed to "trunk". Until we release a 0.1 version (soon™) or Cargo updates to use any HEAD branch name, please update your projects to use this dependency (or equivalent):

```toml
[dependencies]
twilight = { branch = "trunk", git = "https://github.com/twilight-rs/twilight" }
```