message: Clean up tokio-postgres example a bit
diff: //! # Example
  //!
  //! ```no_run
  -//! use futures::FutureExt;
  //! use tokio_postgres::{NoTls, Error, Row};
  //!
  //! # #[cfg(not(feature = "runtime"))] fn main() {}
  //!
  //! // The connection object performs the actual communication with the database,
  //! // so spawn it off to run on its own.
  -//! let connection = connection.map(|r| {
  -//! if let Err(e) = r {
  +//! tokio::spawn(async move {
  +//! if let Err(e) = connection.await {
  //! eprintln!("connection error: {}", e);
  //! }
  //! });
  -//! tokio::spawn(connection);
  //!
  //! // Now we can prepare a simple statement that just returns its parameter.
  //! let stmt = client.prepare("SELECT $1::TEXT").await?;
  //!
  -//! // And then execute it, returning a Stream of Rows which we collect into a Vec.
  -//! let rows: Vec<Row> = client
  +//! // And then execute it, returning a list of the resulting rows.
  +//! let rows = client
  //! .query(&stmt, &[&"hello world"])
  //! .await?;
  //!
  