Update README.md

Corrections link to stable docs

Author: theogf

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.com/JuliaGaussianProcesses/KernelFunctions.jl.svg?branch=master)](https://travis-ci.com/JuliaGaussianProcesses/KernelFunctions.jl)
 [![Coverage Status](https://coveralls.io/repos/github/JuliaGaussianProcesses/KernelFunctions.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaGaussianProcesses/KernelFunctions.jl?branch=master)
-[![Documentation (stable)](https://img.shields.io/badge/docs-stable-blue.svg)](https://juliagaussianprocesses.github.io/KernelFunctions.jl/stable)
+[![Documentation (stable)](https://img.shields.io/badge/docs-stable-blue.svg)](https://juliagaussianprocesses.github.io/KernelFunctions.jl)
 [![Documentation (latest)](https://img.shields.io/badge/docs-dev-blue.svg)](https://juliagaussianprocesses.github.io/KernelFunctions.jl/dev)
 
 ## Kernel functions for machine learning