Prepare next release

Author: williamdes

CHANGELOG.md

@@ -4,6 +4,8 @@ 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).
 
+## [1.x.x] - YYYY-MM-DD
+
 ## [1.3.0] - 2020-11-29
 
 - Fix `OutputFormat::checkOutputFormatIsValid`