Update CHANGELOG to add write_and_append lint

Author: GuillaumeGomez

CHANGELOG.md

@@ -5664,6 +5664,7 @@ Released 2018-09-13
 [`wildcard_enum_match_arm`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_enum_match_arm
 [`wildcard_imports`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_imports
 [`wildcard_in_or_patterns`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_in_or_patterns
+[`write_and_append`]: https://rust-lang.github.io/rust-clippy/master/index.html#write_and_append
 [`write_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#write_literal
 [`write_with_newline`]: https://rust-lang.github.io/rust-clippy/master/index.html#write_with_newline
 [`writeln_empty_string`]: https://rust-lang.github.io/rust-clippy/master/index.html#writeln_empty_string