Update only if wanted version is not available

appveyor.yml

@@ -9,8 +9,14 @@ platform:
   - x86
   - x64
 install:
-  # https://www.appveyor.com/docs/lang/nodejs-iojs/#installing-any-version-of-nodejs-or-iojs
-  - ps: Update-NodeJsInstallation (Get-NodeJsLatestBuild $env:nodejs_version) $env:PLATFORM
+  # https://github.com/appveyor/ci/issues/2921#issuecomment-501016533
+  - ps: |
+      try {
+      Install-Product node $env:nodejs_version $env:platform
+      } catch {
+      echo "Unable to install node $env:nodejs_version, trying update..."
+      Update-NodeJsInstallation (Get-NodeJsLatestBuild $env:nodejs_version) $env:platform
+      }
   - md public
   - npm --vs2015 install --global windows-build-tools
   - npm install