Adding min & max on a frame, update NuGet

 * The NuGet update is the same as here: https://github.com/BlueMountainCapital/FSharpRProvider/pull/116

 * I also added `Stats.min` and `Stats.max` that work on frames - previously, we only had min and max operations on a series (I have no idea how we could miss those in version 1.0...)