chore: update readme badge to reflect move to circleci (#942)

Author: CaerusKaru

README.md

@@ -1,7 +1,7 @@
 # Angular Flex-Layout  
 
 [![npm version](https://badge.fury.io/js/%40angular%2Fflex-layout.svg)](https://www.npmjs.com/package/%40angular%2Fflex-layout)
-[![Build Status](https://travis-ci.org/angular/flex-layout.svg?branch=master)](https://travis-ci.org/angular/flex-layout)
+[![Build status](https://circleci.com/gh/angular/flex-layout.svg?style=svg)](https://circleci.com/gh/angular/flex-layout)
 [![Gitter](https://badges.gitter.im/angular/flex-layout.svg)](https://gitter.im/angular/flex-layout)
 
 Angular Flex Layout provides a sophisticated layout API using Flexbox CSS + mediaQuery.