Target .NET Core 3.0 for unit test project

Author: rthome

SharpNoise.Tests/SharpNoise.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
     <IsPackable>false</IsPackable>
     <Version>0.12.1.0</Version>
     <Authors>Raffael Thome</Authors>