Don't build net461 (or package things) on Linux

Directory.Build.props

@@ -4,7 +4,8 @@
     <Copyright>2017 Stack Exchange, Inc.</Copyright>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <LibTargetFrameworks>net461;netstandard2.0</LibTargetFrameworks>
+    <LibTargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net461;netstandard2.0</LibTargetFrameworks>
+    <LibTargetFrameworks Condition="'$(OS)' != 'Windows_NT'">netstandard2.0</LibTargetFrameworks>
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)StackExchange.Redis.snk</AssemblyOriginatorKeyFile>
     <PackageId>$(AssemblyName)</PackageId>
     <Features>strict</Features>

appveyor.yml

@@ -72,7 +72,7 @@ build_script:
     if ($env:OS -eq "Windows_NT") {
       .\build\dotnet-install.ps1 -Version 2.1.400
     }
-- ps: .\build.ps1 -PullRequestNumber "$env:APPVEYOR_PULL_REQUEST_NUMBER" -CreatePackages $true
+- ps: .\build.ps1 -PullRequestNumber "$env:APPVEYOR_PULL_REQUEST_NUMBER" -CreatePackages ($env:OS -eq "Windows_NT")
 
 test: off
 artifacts: