added CircleCI badge

Author: narciszait

README.md

@@ -4,6 +4,7 @@
 A small (but cool) tool for handling UIKeyboard appearing and disappearing in your view controllers.
 
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 [![Codecov](https://img.shields.io/codecov/c/github/nodes-ios/KeyboardHelper.svg)](https://codecov.io/github/nodes-ios/KeyboardHelper)
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