(feat):update objective-c sdk with coverals (#368)

* update objective-c sdk with coverals

* remove extra brackets

Author: thomaszurkan-optimizely

README.md

@@ -2,6 +2,7 @@
 [![Build Status](https://travis-ci.org/optimizely/objective-c-sdk.svg?branch=master)](https://travis-ci.org/optimizely/objective-c-sdk/)
 [![Apache 2.0](https://img.shields.io/github/license/nebula-plugins/gradle-extra-configurations-plugin.svg)](http://www.apache.org/licenses/LICENSE-2.0)
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/carthage/carthage)
+![Coveralls](https://img.shields.io/coveralls/optimizely/objective-c-sdk.svg)
 ![Platforms](https://img.shields.io/cocoapods/p/OptimizelySDKiOS.svg)
 [![Podspec](https://img.shields.io/cocoapods/v/OptimizelySDKiOS.svg)](https://cocoapods.org/pods/OptimizelySDKiOS)
 ![Platforms](https://img.shields.io/cocoapods/p/OptimizelySDKTVOS.svg)