Revert to .Net 4.6.1

[BPotocki]

Would you be opposed to reverting .Net versions from 4.7.2 to 4.6.1? It looks like it was updated across the board in this commit, and the nuspec was fixed here to go along with it.

The updates don't seem to actually require 4.7.2 however (only based on a local build succeeding, I could be wrong), so I'm wondering if reverting could be done to expand compatibility with those of us who aren't on the latest and greatest :)