update README.md

- include travis and codecov badges
- remove the github issue badge

Author: Yue-Jiang

README.md

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 # randomForestExplainer
 
 [![CRAN_Status_Badge](http://www.r-pkg.org/badges/version/randomForestExplainer)](https://cran.r-project.org/package=randomForestExplainer)
-[![Github Issues](http://githubbadges.herokuapp.com/ModelOriented/randomForestExplainer/issues.svg)](https://github.com/MI2DataLab/ModelOriented/issues)
+[![Build Status](https://travis-ci.org/ModelOriented/randomForestExplainer.svg?branch=master)](https://travis-ci.org/ModelOriented/randomForestExplainer)
+[![codecov](https://codecov.io/gh/ModelOriented/randomForestExplainer/branch/master/graph/badge.svg)](https://codecov.io/gh/ModelOriented/randomForestExplainer)
 [![DOI](https://zenodo.org/badge/97007621.svg)](https://zenodo.org/badge/latestdoi/97007621)
 
 A set of tools to understand what is happening inside a Random Forest. A detailed discussion of the package and importance measures it implements can be found here: [Master thesis on randomForestExplainer](https://rawgit.com/geneticsMiNIng/BlackBoxOpener/master/randomForestExplainer_Master_thesis.pdf).