Rollup merge of #79351 - Takashiidobe:keyword-docs-typo, r=m-ou-se
Rollup merge of #79351 - Takashiidobe:keyword-docs-typo, r=m-ou-se

Fix typo in `keyword` docs for traits

This PR fixes a small typo in the `keyword_docs.rs` file, describing the differences between the 2015 and 2018 editions of traits.

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