Add macos build badge [skip ci]
| OS | Build-Status |
| - |:- |
| linux | [![CircleCI](https://circleci.com/gh/Bios-Marcel/cordless.svg?style=svg)](https://circleci.com/gh/Bios-Marcel/cordless) |
-| darwin | TODO |
+| darwin | [![Build Status](https://travis-ci.org/Bios-Marcel/cordless.svg?branch=master)](https://travis-ci.org/Bios-Marcel/cordless) |
| windows | [![Build status](https://ci.appveyor.com/api/projects/status/svv866htsr33hdoh/branch/master?svg=true)](https://ci.appveyor.com/project/Bios-Marcel/cordless/branch/master) |
## Overview
