Updates status badges (#487)

* Updates status badges

- This is part of a series of commits across the
   repositories to update badges and branding.

* Adds `next patch` badge

README.md

-Npgsql Entity Framework Core provider for PostgreSQL
-=============
+# Npgsql Entity Framework Core provider for PostgreSQL
 
-[![Stable NuGet](https://img.shields.io/nuget/v/Npgsql.EntityFrameworkCore.PostgreSQL.svg?label=stable%20nuget)](https://www.nuget.org/packages/Npgsql.EntityFrameworkCore.PostgreSQL) [![Unstable MyGet](https://img.shields.io/myget/npgsql-unstable/v/Npgsql.EntityFrameworkCore.PostgreSQL.svg?label=unstable%20myget)](https://www.myget.org/feed/npgsql-unstable/package/nuget/Npgsql.EntityFrameworkCore.PostgreSQL) [![Join the chat at https://gitter.im/npgsql/npsgl](https://img.shields.io/badge/gitter-join%20chat-brightgreen.svg)](https://gitter.im/npgsql/npgsql)
+[![stable](https://img.shields.io/nuget/v/Npgsql.EntityFrameworkCore.PostgreSQL.svg?label=stable)](https://www.nuget.org/packages/Npgsql.EntityFrameworkCore.PostgreSQL/) [![unstable](https://img.shields.io/myget/npgsql-unstable/vpre/Npgsql.EntityFrameworkCore.PostgreSQL.svg?label=unstable)](https://www.myget.org/feed/npgsql-unstable/package/nuget/Npgsql.EntityFrameworkCore.PostgreSQL) [![next patch](https://img.shields.io/myget/npgsql/v/Npgsql.EntityFrameworkCore.PostgreSQL.svg?label=next%20patch)](https://www.myget.org/feed/npgsql/package/nuget/Npgsql.EntityFrameworkCore.PostgreSQL)
+[![appveyor](https://img.shields.io/appveyor/ci/roji/npgsql-entityframeworkcore-postgresql/dev.svg?label=appveyor)](https://ci.appveyor.com/project/roji/npgsql-entityframeworkcore-postgresql) [![travis](https://img.shields.io/travis/npgsql/npgsql.svg?label=travis)](https://travis-ci.org/npgsql/Npgsql.EntityFrameworkCore.PostgreSQL) [![gitter](https://img.shields.io/badge/gitter-join%20chat-brightgreen.svg)](https://gitter.im/npgsql/npgsql)
 
 Npgsql.EntityFrameworkCore.PostgreSQL is an Entity Framework Core provider built on top of
 [Npgsql](https://github.com/npgsql/npgsql). It allows you to use the EF Core O/RM with