message: Bump version in readme
diff: @@ -8,7 +8,7 @@ A native PostgreSQL driver for Rust.
  You can integrate Rust-Postgres into your project through the [releases on crates.io](https://crates.io/crates/postgres):
  ```toml
  [dependencies]
  -postgres = "0.14"
  +postgres = "0.15"
  ```
  ## Overview
  