check update is now working on macos Sierra

[Dirk Hohndel]

Turns out that macos no longer identifies itself as OS X but now calls
itself macOS. The backend server didn't know what to do with that and sent
back a rather pointless "Thank You". This has now been fixed in two ways:

a) it recognizes Sierra as being a Mac
b) instead of saying "Thank You" it asks the user to please contact us so
we can figure out why the update check isn't working

/D