Upgraded the project to .NET Core 3

Author: Zarbuz

SchematicToVoxCore/FileToVox.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
     <StartupObject>FileToVox.Program</StartupObject>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
     <RuntimeIdentifiers>win-x64;linux-x64;osx-x64</RuntimeIdentifiers>