Merge pull request #20 from richpsharp/release/0.9

fixes #19 adding a note in history that this is the release

Author: phargogh

HISTORY.rst

@@ -4,7 +4,7 @@
 TaskGraph Release History
 =========================
 
-Unreleased Changes
+0.9.0 (2020-03-05)
 ------------------
 * Updating primary repository URL to GitHub.
 * Adding support for Python 3.8.