title: Dot symbol in docker compose environment variables doesn't work
body: <p>I have a docker-compose file with environment variables set like:</p>
  <pre><code> identity-api:
      environment:
        - ASPNETCORE_ENVIRONMENT=Development
        - ASPNETCORE_URLS=http://0.0.0.0:80
        - SpaClient=http://${ESHOP_EXTERNAL_DNS.NAME_OR_IP}:5104
  </code></pre>
  <p>It's just an example from <a href="https://github.com/dotnet-architecture/eShopOnContainers/blob/dev/src/docker-compose.override.yml" rel="nofollow noreferrer">https://github.com/dotnet-architecture/eShopOnContainers/blob/dev/src/docker-compose.override.yml</a>.</p>
  <p>The issue: I replaced underscore symbol with dot symbol here: <code>ESHOP_EXTERNAL_DNS_NAME_OR_IP</code> -&gt; <code>ESHOP_EXTERNAL_DNS.NAME_OR_IP</code>.
  After that, If I try to build docker-compose project in VS, it will not work. The error looks like:</p>
  <pre><code>Error   DT1001  Invalid interpolation format for &quot;environment&quot; option in service &quot;identity-api&quot;:&quot;SpaClient=http://${ESHOP_EXTERNAL_DNS.NAME_OR_IP}:5104&quot;    
  docker-compose  C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Sdks\Microsoft.Docker.Sdk\build\Microsoft.VisualStudio.Docker.Compose.targets 202 
  </code></pre>
  <p>So the question: what is wrong with the variable name here? Is dot symbol supported or not? Or maybe it can be escaped somehow?</p>