fullcheck.ps1: add nightly

fullcheck.ps1

 $ErrorActionPreference = "Stop"
-ForEach ($r in "lts-9","lts-11","lts-12","lts-14","lts-15")
+ForEach ($r in "lts-9","lts-11","lts-12","lts-14","lts-15","nightly")
 {
 	& "stack" "--resolver" "$r" "build"
 	if (!$?) {Exit 1}