v4: Repository shouldnt link to local nuget server

[bielu]

Hi @zpqrtbnk,
One of my coworkers remind about issue which I had when work with this repo.
We shouldn't include any depedency on not publicly available nuget feeds:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="UmbracoCoreMyGet" value="https://www.myget.org/F/umbracocore/api/v3/index.json" />
    <add key="nuget.local" value="http://nuget.local/nuget/" />
  </packageSources>
</configuration>

should be:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="UmbracoCoreMyGet" value="https://www.myget.org/F/umbracocore/api/v3/index.json" />
  </packageSources>
</configuration>