message: changelog: start changelog for 1.1.3 release
diff: +1.1.3 (2019-03-30)
  +==================
  +This releases fixes a few bugs and adds a performance improvement when a regex
  +is a simple alternation of literals.
  +
  +Performance improvements:
  +
  +* [OPT #566](https://github.com/rust-lang/regex/pull/566):
  + Upgrades `aho-corasick` to 0.7 and uses it for `foo|bar|...|quux` regexes.
  +
  +
  1.1.2 (2019-02-27)
  ==================
  This release fixes a bug found in the fix introduced in 1.1.1.
  