update readme

Author: bensadeghi

README.md

@@ -2,10 +2,7 @@
 
 [![Build Status](https://travis-ci.org/bensadeghi/DecisionTree.jl.svg?branch=master)](https://travis-ci.org/bensadeghi/DecisionTree.jl)
 [![Coverage Status](https://coveralls.io/repos/bensadeghi/DecisionTree.jl/badge.svg?branch=master)](https://coveralls.io/r/bensadeghi/DecisionTree.jl?branch=master)
-
-[![DecisionTree](http://pkg.julialang.org/badges/DecisionTree_0.5.svg)](http://pkg.julialang.org/?pkg=DecisionTree&ver=0.5)
-[![DecisionTree](http://pkg.julialang.org/badges/DecisionTree_0.6.svg)](http://pkg.julialang.org/?pkg=DecisionTree&ver=0.6)
-[![DecisionTree](http://pkg.julialang.org/badges/DecisionTree_0.7.svg)](http://pkg.julialang.org/?pkg=DecisionTree&ver=0.7)
+[![Docs Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://pkg.julialang.org/docs/DecisionTree/pEDeB/0.8.1/)
 
 Julia implementation of Decision Tree and Random Forest algorithms