Test workaround for SSL issue.

appveyor.yml

@@ -88,7 +88,7 @@ install:
         Where-Object pullRequestId -eq $env:APPVEYOR_PULL_REQUEST_NUMBER)[0].buildNumber) { `
           throw "There are newer queued builds for this pull request, failing early." }
 
-  - ps: [Net.ServicePointManager]::SecurityProtocol = 'Ssl3, Tls, Tls11, Tls12'
+  - ps: "[System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Tls12"
 
   # Install Python (from the official .msi of http://python.org) and pip when
   # not already installed.