Update README.md

Added a security shield from Hakiri. It shows how secure gem dependencies are.

README.md

 Paperclip
 Paperclip
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-[![Build Status](https://secure.travis-ci.org/thoughtbot/paperclip.png?branch=master)](http://travis-ci.org/thoughtbot/paperclip) [![Dependency Status](https://gemnasium.com/thoughtbot/paperclip.png?travis)](https://gemnasium.com/thoughtbot/paperclip) [![Code Climate](https://codeclimate.com/github/thoughtbot/paperclip.png)](https://codeclimate.com/github/thoughtbot/paperclip) [![Inline docs](http://inch-ci.org/github/thoughtbot/paperclip.png)](http://inch-ci.org/github/thoughtbot/paperclip)
+[![Build Status](https://secure.travis-ci.org/thoughtbot/paperclip.png?branch=master)](http://travis-ci.org/thoughtbot/paperclip) [![Dependency Status](https://gemnasium.com/thoughtbot/paperclip.png?travis)](https://gemnasium.com/thoughtbot/paperclip) [![Code Climate](https://codeclimate.com/github/thoughtbot/paperclip.png)](https://codeclimate.com/github/thoughtbot/paperclip) [![Inline docs](http://inch-ci.org/github/thoughtbot/paperclip.png)](http://inch-ci.org/github/thoughtbot/paperclip) [![Security](https://hakiri.io/github/thoughtbot/paperclip/master.svg)](https://hakiri.io/github/thoughtbot/paperclip/master)
 
 
 Paperclip is intended as an easy file attachment library for Active Record. The
 Paperclip is intended as an easy file attachment library for Active Record. The
 intent behind it was to keep setup as easy as possible and to treat files as
 intent behind it was to keep setup as easy as possible and to treat files as