message: fix wrong badge
diff: # HermitCore - A lightweight unikernel for a scalable and predictable runtime behavior
  -[![Build Status](https://travis-ci.org/RWTH-OS/HermitCore.svg?branch=master)](https://travis-ci.org/RWTH-OS/HermitCore)
  +[![Build Status](https://travis-ci.org/RWTH-OS/HermitCore.svg?branch=devel)](https://travis-ci.org/RWTH-OS/HermitCore)
  [![Slack Status](https://radiant-ridge-95061.herokuapp.com/badge.svg)](https://radiant-ridge-95061.herokuapp.com)
  The project [HermitCore]( http://www.hermitcore.org ) is a new
  