update CHANGELOG

CHANGELOG.md

+<!--
+## 0.x.x (unreleased)
 
+### :sparkles: Improvements
+
+### :gem: Features
+
+### :bug: Bugfixes
+
+-->
+
+## 0.20.0 (unreleased)
+
+### :sparkles: Improvements
+- Add a property to the URL node indicating whether it was enclosed in `<>` (#69)
+- Disallow `<` and `>` in hashtags. (#74)
+- Mentions in the link label are parsed as text. (#66)
+
+### :gem: Features
+- Add tag syntaxes of bold and strikethrough (#76)
+
+## 0.19.0
+
+npm: https://www.npmjs.com/package/mfm-js/v/0.19.0
+
+### :sparkles: Improvements
+- Parser: Ignores a blank line after quote lines. (#61) 
+
+## 0.18.0
+
+npm: https://www.npmjs.com/package/mfm-js/v/0.18.0
+
+### :sparkles: Improvements
+- Twemoji v13.1 is supported.