Point Travis badge to proper branch

Author: helje5

README.md

@@ -3,7 +3,7 @@
 ![Swift4](https://img.shields.io/badge/swift-4-blue.svg)
 ![macOS](https://img.shields.io/badge/os-macOS-green.svg?style=flat)
 ![tuxOS](https://img.shields.io/badge/os-tuxOS-green.svg?style=flat)
-![Travis](https://travis-ci.org/NozeIO/swift-nio-redis.svg?branch=develop)
+![Travis](https://travis-ci.org/NozeIO/swift-nio-redis.svg?branch=master)
 
 SwiftNIO Redis is a Swift package that contains a high performance 
 [Redis protocol](https://redis.io/topics/protocol)