clippy 0.0.302

A bunch of helpful lints to avoid common pitfalls in Rust.
Installing clippy via crates.io is deprecated. Please use the following:

```terminal
rustup component add clippy-preview
```

on a Rust version 1.29 or later. You may need to run `rustup self update` if it complains about a missing clippy binary.

See [the homepage](https://github.com/rust-lang-nursery/rust-clippy/#clippy) for more information