message: Fix tokio features for runtime feature in the docs
diff: //!
  //! | Feature | Description | Extra dependencies | Default |
  //! | ------- | ----------- | ------------------ | ------- |
  -//! | `runtime` | Enable convenience API for the connection process based on the `tokio` crate. | [tokio](https://crates.io/crates/tokio) 0.2 with the features `dns`, `net` and `time` | yes |
  +//! | `runtime` | Enable convenience API for the connection process based on the `tokio` crate. | [tokio](https://crates.io/crates/tokio) 0.3 with the `io-util` feature | yes |
  //! | `with-bit-vec-0_6` | Enable support for the `bit-vec` crate. | [bit-vec](https://crates.io/crates/bit-vec) 0.6 | no |
  //! | `with-chrono-0_4` | Enable support for the `chrono` crate. | [chrono](https://crates.io/crates/chrono) 0.4 | no |
  //! | `with-eui48-0_4` | Enable support for the `eui48` crate. | [eui48](https://crates.io/crates/eui48) 0.4 | no |
  //! | `with-serde_json-1` | Enable support for the `serde_json` crate. | [serde_json](https://crates.io/crates/serde_json) 1.0 | no |
  //! | `with-uuid-0_8` | Enable support for the `uuid` crate. | [uuid](https://crates.io/crates/uuid) 0.8 | no |
  //! | `with-time-0_2` | Enable support for the `time` crate. | [time](https://crates.io/crates/time) 0.2 | no |
  -#![doc(html_root_url = "https://docs.rs/tokio-postgres/0.5")]
  +#![doc(html_root_url = "https://docs.rs/tokio-postgres/0.6")]
  #![warn(rust_2018_idioms, clippy::all, missing_docs)]
  pub use crate::cancel_token::CancelToken;
  