Changed HISTORY to include recent changes

HISTORY.md

+## 1.4.0 (TO BE RELEASED)
+
+* GitLab CI support
+* Fixed `.pod` test files to use newer syntax.
+* Changes to support Python 3 (it's not out-of-the box yet, you still need to patch code)
+
 ## 1.3.3 (2015-02-17)
 * Address a slight typo with `POSIX` [#456](https://github.com/github/markup/pull/456)