Update README.md

README.md

@@ -3,7 +3,7 @@ lifelines
 
 [![Latest Version](https://pypip.in/v/lifelines/badge.png)](https://pypi.python.org/pypi/lifelines/)
 [![Build Status](https://travis-ci.org/CamDavidsonPilon/lifelines.svg?branch=master)](https://travis-ci.org/CamDavidsonPilon/lifelines)
-[![Coverage Status](https://coveralls.io/repos/CamDavidsonPilon/lifelines/badge.svg)](https://coveralls.io/r/CamDavidsonPilon/lifelines)
+[![Coverage Status](https://coveralls.io/repos/CamDavidsonPilon/lifelines/badge.svg?branch=master)](https://coveralls.io/r/CamDavidsonPilon/lifelines?branch=master)
 
 [What is survival analysis and why should I learn it?](http://lifelines.readthedocs.org/en/latest/Survival%20Analysis%20intro.html)
  Survival analysis was originally developed and applied heavily by the actuarial and medical community. Its purpose was to answer *why do events occur now versus later* under uncertainty (where *events* might refer to deaths, disease remission, etc.). This is great for researchers who are interested in measuring lifetimes: they can answer questions like *what factors might influence deaths?*