switch back to netcoreapp2.1 for Tests

Author: Mpdreamz

src/Tests/Tests/Tests.csproj

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net462</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
     <VersionPrefix>6.0.0</VersionPrefix>
     <VersionSuffix>alpha</VersionSuffix>
     <NoWarn>$(NoWarn);xUnit1013</NoWarn>