Adding a package that references Microsoft.Extensions.Logging.Abstractions breaks function

From @dersia at #293:

> Hi there I just realized, that there seems to be an issue with the new ILogger. If I select the ILogger, everything works as expected and there is no issue at all, but if I consume a nuget-package which has dependency on Microsoft.Extensions.Logging.Abstractions it stops working. I actually get a failure upon loading the function:
>
> Microsoft.Azure.WebJobs.Host: Cannot bind parameter 'log' to type ILogger. Make sure the parameter Type is supported by the binding. If you're using binding extensions (e.g. ServiceBus, Timers, etc.) make sure you've called the registration method for the extension(s) in your startup code (e.g. config.UseServiceBus(), config.UseTimers(), etc.)