Update README.md [skip ci]

Author: Aragas

README.md

@@ -1,4 +1,4 @@
-**Mono & .NET Core:** | **.NET 4.5 & .NET Core:** | **NuGet** | **Codecov** | **COVERALLS**
+**Mono & .NET Core:** | **.NET 4.5 & .NET Core:** | **NuGet** | **Coveralls** | **Codecov**
 ------------ | ------------- | ------------- | ------------- | -------------
  | [![Build Status](https://travis-ci.org/PCLExt/PCLExt.FileStorage.svg?branch=master)](https://travis-ci.org/PCLExt/PCLExt.FileStorage) | [![Build status](https://ci.appveyor.com/api/projects/status/puku2ym0k1n7ryde?svg=true)](https://ci.appveyor.com/project/Aragas/pclext-filestorage) [![AppVeyor tests](https://img.shields.io/appveyor/tests/Aragas/pclext-filestorage.svg)]() | [![NuGet](https://img.shields.io/nuget/v/PCLExt.FileStorage.svg)](https://www.nuget.org/packages/PCLExt.FileStorage/) | [![Coverage Status](https://coveralls.io/repos/github/PCLExt/PCLExt.FileStorage/badge.svg?branch=master)](https://coveralls.io/github/PCLExt/PCLExt.FileStorage?branch=master) | [![codecov](https://codecov.io/gh/PCLExt/PCLExt.FileStorage/branch/master/graph/badge.svg)](https://codecov.io/gh/PCLExt/PCLExt.FileStorage)