Update README.md

Author: aldobrynin

README.md

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 # GroBuf
 
 [![NuGet Status](https://img.shields.io/nuget/v/GroBuf.svg)](https://www.nuget.org/packages/GroBuf/)
-[![Build Status](https://travis-ci.org/skbkontur/GroBuf.svg?branch=master)](https://travis-ci.org/skbkontur/GroBuf)
-[![Build status](https://ci.appveyor.com/api/projects/status/xbq92fnsfbo8946k?svg=true)](https://ci.appveyor.com/project/skbkontur/grobuf)
+[![Build status](https://github.com/skbkontur/GroBuf/actions/workflows/actions.yml/badge.svg)](https://github.com/skbkontur/GroBuf/actions)
+
 
 GroBuf is a fast binary serializer for .NET.