6.11.1

[6.11.1] - 2019-11-21

Fixed:

• Fixed an incompatibility with Python 3.3 due to an unpinned dependency on expiringdict.
• Fixed usages that caused a SyntaxWarning in Python 3.8. (Thanks, bunchesofdonald!)
• Updated CI scripts so a SyntaxWarning will always cause a build failure, and added a 3.8 build.