add test fixtures to sdist

Author: mmlb

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+### Added
+- Test fixtures to sdist
+
 ## [1.38.1] - 2019-05-30
 ### Fixed
 - Changelog

MANIFEST.in

@@ -1,2 +1,3 @@
 include CHANGELOG.md
 include README.md
+include test/fixtures/*.json