Rollup merge of #37081 - p512:master, r=sfackler
Rollup merge of #37081 - p512:master, r=sfackler

Changed 0 into '0'

Right now `0` is an undefined production rule.
[Documentation following the grammar specification](https://doc.rust-lang.org/nightly/std/fmt/#sign0) strongly suggests `'0'` is meant as it is used as a character literal.

r? @steveklabnik

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