Use version range for Serilog dependencies

I've been bitten twice by this: https://github.com/intuit/QuickBooks-V3-DotNET-SDK/issues/225#issuecomment-1209966318
I agree with the suggestion in #221 that removing references to Serilog entirely is a good direction for a library project to take.

In the meantime, some of the developer pain could be avoided by declaring a [version range](https://docs.microsoft.com/en-us/nuget/concepts/package-versioning#examples) in the Nuget package.

Instead of

```xml

```

I suggest

```xml

```