Match CI shield style

Author: damieng

docs/build-instructions/build-status.md

@@ -2,7 +2,7 @@
 
 | System | Travis | AppVeyor/Win | Circle/Mac | Dependencies |
 |--------|--------|--------------|------------|--------------|
-| [Atom](https://github.com/atom/atom)   | [![Travis Build Status](https://travis-ci.org/atom/atom.svg?branch=master)](https://travis-ci.org/atom/atom) | [![AppVeyor/Wi Build Status](https://ci.appveyor.com/api/projects/status/1tkktwh654w07eim?svg=true)](https://ci.appveyor.com/project/Atom/atom) | [![Circle/Mac Build Status](https://circleci.com/gh/atom/atom.svg?style=svg)](https://circleci.com/gh/atom/atom) | [![Dependency Status](https://david-dm.org/atom/atom.svg)](https://david-dm.org/atom/atom) |
+| [Atom](https://github.com/atom/atom)   | [![Travis Build Status](https://travis-ci.org/atom/atom.svg?branch=master)](https://travis-ci.org/atom/atom) | [![AppVeyor/Wi Build Status](https://ci.appveyor.com/api/projects/status/1tkktwh654w07eim?svg=true)](https://ci.appveyor.com/project/Atom/atom) | [![Circle/Mac Build Status](https://circleci.com/gh/atom/atom.svg?style=shield)](https://circleci.com/gh/atom/atom) | [![Dependency Status](https://david-dm.org/atom/atom.svg)](https://david-dm.org/atom/atom) |
 | [APM](https://github.com/atom/apm) | [![Travis Build Status](https://travis-ci.org/atom/apm.svg?branch=master)](https://travis-ci.org/atom/apm) | [![AppVeyor/Wi Build Status](https://ci.appveyor.com/api/projects/status/j6ixw374a397ugkb/branch/master?svg=true)](https://ci.appveyor.com/project/Atom/apm/branch/master) | | [![Dependency Status](https://david-dm.org/atom/apm.svg)](https://david-dm.org/atom/apm) |
 | [Electron](https://github.com/electron/electron) | [![Travis Build Status](https://travis-ci.org/electron/electron.svg?branch=master)](https://travis-ci.org/electron/electron) | [![AppVeyor/Wi Build Status](https://ci.appveyor.com/api/projects/status/kvxe4byi7jcxbe26/branch/master?svg=true)](https://ci.appveyor.com/project/Atom/electron) | | [![Dependency Status](https://david-dm.org/electron/electron/dev-status.svg)](https://david-dm.org/electron/electron)