Add explicit System.Net.Primitives reference for CrossGen

Author: alrod

src/WebJobs.Script/WebJobs.Script.csproj

@@ -50,6 +50,7 @@
     <PackageReference Include="System.IO.Abstractions" Version="2.1.0.175">
       <NoWarn>NU1701</NoWarn>
     </PackageReference>
+    <PackageReference Include="System.Net.Primitives" Version="4.3.0" />
     <PackageReference Include="System.Reactive.Linq" Version="3.1.1" />
     <PackageReference Include="System.Reactive.PlatformServices" Version="3.1.1" />
     <PackageReference Include="System.Reflection.Emit" Version="4.3.0" />