Remove old, redundant DNX relict (#912)

Author: bergmeister

Rules/Rules.csproj

@@ -5,7 +5,7 @@
     <TargetFrameworks>netstandard1.6;net451</TargetFrameworks>
     <AssemblyName>Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules</AssemblyName>
     <PackageId>Rules</PackageId>
-    <PackageTargetFallback Condition=" '$(TargetFramework)' == 'netstandard1.6' ">$(PackageTargetFallback);dnxcore50</PackageTargetFallback>
+    <PackageTargetFallback Condition=" '$(TargetFramework)' == 'netstandard1.6' ">$(PackageTargetFallback)</PackageTargetFallback>
     <RuntimeFrameworkVersion Condition=" '$(TargetFramework)' == 'netstandard1.6' ">1.0.4</RuntimeFrameworkVersion>
     <RootNamespace>Microsoft.Windows.PowerShell.ScriptAnalyzer</RootNamespace> <!-- Namespace needs to match Assembly name for ressource binding -->
   </PropertyGroup>