updated Changelog

ChangeLog.md

 # Change Log
 All notable changes to this project will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased](https://github.com/nlohmann/json/tree/HEAD)
+
+[Full Changelog](https://github.com/nlohmann/json/compare/v2.0.1...HEAD)
+
+- Build error for std::int64 [\#282](https://github.com/nlohmann/json/issues/282)
+
+- hexify\(\) function emits conversion warning [\#270](https://github.com/nlohmann/json/issues/270)
+
+- let the makefile choose the correct sed [\#279](https://github.com/nlohmann/json/pull/279) ([murinicanor](https://github.com/murinicanor))
+- Update hexify to use array lookup instead of ternary \(\#270\) [\#275](https://github.com/nlohmann/json/pull/275) ([dtoma](https://github.com/dtoma))
+
 ## [v2.0.1](https://github.com/nlohmann/json/releases/tag/v2.0.1) (2016-06-28)
 [Full Changelog](https://github.com/nlohmann/json/compare/v2.0.0...v2.0.1)