Fix code generation problems with .NET Core 3.1
Workaround for problem described in #20
- The .NET Core 3.1 driver was getting .NET Core 3.0 references, which prevented it from compiling the generated code because the driver itself was a reference and therefore needed 3.1 references.
- As a workaround, the driver is no longer a required reference for the generated code, which is compatible with either .NET Core 3.0 or 3.1, so no matter what runtime LinqPad provides, the code should compile.