Rollup merge of #57179 - Xaeroxe:patch-1, r=QuietMisdreavus
Rollup merge of #57179 - Xaeroxe:patch-1, r=QuietMisdreavus

Update std/lib.rs docs to reflect Rust 2018 usage

Fixes #56544

This paragraph was written for Rust 2015.  Since 2018 has been stable for a while I think we can update it.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust