Update 1.13 badge in the README

README.md

 # MicroK8s
 
-![](https://img.shields.io/badge/Kubernetes-1.12-326de6.svg) ![Build Status](https://travis-ci.org/ubuntu/microk8s.svg)
+![](https://img.shields.io/badge/Kubernetes-1.13-326de6.svg) ![Build Status](https://travis-ci.org/ubuntu/microk8s.svg)
 
 <img src="https://raw.githubusercontent.com/cncf/artwork/master/kubernetes/certified-kubernetes/versionless/color/certified-kubernetes-color.png" align="right" width="200px">Kubernetes in a [snap](https://snapcraft.io/) that you can run locally.
 
@@ -212,4 +212,4 @@ snap install microk8s_v1.10.3_amd64.snap --classic --dangerous
 
 <p align="center">
   <img src="https://assets.ubuntu.com/v1/9309d097-MicroK8s_SnapStore_icon.svg" width="150px">
-</p>
\ No newline at end of file
+</p>