Add Travis badge

Author: Zuzanna Stolińska

Diff for: README.md

@@ -1,7 +1,9 @@
-# SwaggerUiEngine
+# SwaggerUiEngine 
 
 Include [swagger-ui](https://github.com/swagger-api/swagger-ui) as Rails engine and document your API with simple YAML files.
 
+[![Build Status](https://travis-ci.org/ZuzannaSt/swagger_ui_engine.svg?branch=master)](https://travis-ci.org/ZuzannaSt/swagger_ui_engine)
+
 ## Versions
 
 Swagger UI version | Rails version