Reverted to original fast-fail for AppVeyor

Changes to simplify AppVeyor’s fast-fail solution borrowed from
JuliaLang may not have worked. Reverting to ensure that it is not an
outstanding issue.

utils/appveyor-killold.ps1

@@ -10,10 +10,11 @@
 # The AppVeyor 'rollout builds' option is supposed to serve the same
 # purpose but it is problematic because it tends to cancel builds pushed
 # directly to master instead of just PR builds (or the converse).
-# credits: JuliaLang developers.
-$_NEWEST = "https://ci.appveyor.com/api/projects/${env:APPVEYOR_ACCOUNT_NAME}/${env:APPVEYOR_PROJECT_SLUG}/history?recordsNumber=50"
-$_NEWEST = ((Invoke-RestMethod $_NEWEST).builds | Where-Object pullRequestId)
-$_NEWEST = ($_NEWEST -Eq $env:APPVEYOR_PULL_REQUEST_NUMBER)[0].buildNumber
-if ($env:APPVEYOR_PULL_REQUEST_NUMBER -And $env:APPVEYOR_BUILD_NUMBER -Ne $_NEWEST) {
+# reference:
+#   JuliaLang developers
+#   (https://github.com/JuliaLang/Example.jl/commit/8a4959122ce843b3664337c8b5119ce3a968c408)
+if ($env:APPVEYOR_PULL_REQUEST_NUMBER -and $env:APPVEYOR_BUILD_NUMBER -ne ((Invoke-RestMethod
+    https://ci.appveyor.com/api/projects/$env:APPVEYOR_ACCOUNT_NAME/$env:APPVEYOR_PROJECT_SLUG/history?recordsNumber=50).builds |
+    Where-Object pullRequestId -eq $env:APPVEYOR_PULL_REQUEST_NUMBER)[0].buildNumber) {
     throw "There are newer queued builds for this pull request, failing early."
 }