add travis build status to readme
add travis build status to readme

buaasun/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,uwsampa/grappa,uwsampa/grappa,uwsampa/grappa,alexfrolov/grappa,alexfrolov/grappa,buaasun/grappa,buaasun/grappa,uwsampa/grappa,alexfrolov/grappa,alexfrolov/grappa,buaasun/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,buaasun/grappa,alexfrolov/grappa