Add travis-ci badge

Author: dmaccormack

README.md

@@ -1,5 +1,6 @@
 # JSON->URL
 [![Apache License, Version 2.0, January 2004](https://img.shields.io/github/license/jsonurl/jsonurl-java.svg?label=License)](https://www.apache.org/licenses/LICENSE-2.0)
+[![Build Status](https://travis-ci.com/jsonurl/jsonurl-java.svg?branch=master)](https://travis-ci.com/jsonurl/jsonurl-java)
 [![Known Vulnerabilities](https://snyk.io/test/github/jsonurl/jsonurl-java/badge.svg?targetFile=module/jsonurl-jsonorg/pom.xml)](https://snyk.io/test/github/jsonurl/jsonurl-java?targetFile=module/jsonurl-jsonorg/pom.xml)
 [![Known Vulnerabilities](https://snyk.io/test/github/jsonurl/jsonurl-java/badge.svg?targetFile=module/jsonurl-jsr374/pom.xml)](https://snyk.io/test/github/jsonurl/jsonurl-java?targetFile=module/jsonurl-jsr374/pom.xml)