Add unreleased changelog entry

Author: jayaddison

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+- Drop support for Python versions prior to 3.6
+
 ## [1.0.2](https://github.com/jeancochrane/pytest-flask-sqlalchemy/releases/tag/v1.0.2) (2019-04-03)
 
 ### Changed