Added Travis build status badge

Author: asbjornu

README.md

@@ -7,6 +7,7 @@ Makes it easy to automate git for testing libraries which interact with git. Thi
 ![Version](https://img.shields.io/nuget/v/gittools.testing.svg)
 ![Pre-release version](https://img.shields.io/nuget/vpre/gittools.testing.svg)
 [![Build status](https://ci.appveyor.com/api/projects/status/p43k5vdjqldqavag/branch/master?svg=true)](https://ci.appveyor.com/project/GitTools/gittools-testing/branch/master)
+[![Build Status](https://travis-ci.org/GitTools/GitTools.Testing.svg?branch=master)](https://travis-ci.org/GitTools/GitTools.Testing)
 
 ## Fixtures
 The main purpose for this library, providing test fixtures which wrap a temporary git repository making it super easy to create test scenarios. For example