Remove references to Travis (no longer free, offline for a long time now) (#157)

Author: egonw

.travis.yml

@@ -1,8 +1,6 @@
 
 <!-- README.md is generated from README.Rmd. Please edit that file -->
 
-[![Build
-Status](https://api.travis-ci.org/CDK-R/cdkr.svg?branch=master)](https://travis-ci.org/CDK-R/cdkr)
 [![CRAN
 Version](https://www.r-pkg.org/badges/version/rcdk?color=green)](https://cran.r-project.org/package=rcdk)
 [![CRAN