Download by AppVeyor

* appveyor.yml (install): use AppVeyor command-line utility to
  download files, instead of Start-FileDownload cmdlet which no
  longer works more than once.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56227 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

appveyor.yml

@@ -11,14 +11,14 @@ install:
   - mkdir \usr\local\bin
   - mkdir \usr\local\include
   - mkdir \usr\local\lib
-  - ps: Start-FileDownload 'http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.3.7-windows.zip'
+  - appveyor DownloadFile http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.3.7-windows.zip
   - 7z x libressl-2.3.7-windows.zip
   - copy libressl-2.3.7-windows\x64\libcrypto-37.lib \usr\local\lib\crypto.lib
   - copy libressl-2.3.7-windows\x64\libssl-38.lib    \usr\local\lib\ssl.lib
   - copy libressl-2.3.7-windows\x64\libcrypto-37.dll \usr\local\bin
   - copy libressl-2.3.7-windows\x64\libssl-38.dll    \usr\local\bin
   - xcopy /e libressl-2.3.7-windows\include          \usr\local\include
-  - ps: Start-FileDownload 'http://zlib.net/zlib128.zip'
+  - appveyor DownloadFile http://zlib.net/zlib128.zip
   - 7z x zlib128.zip
   - cd zlib-1.2.8
   - nmake -f win32/Makefile.msc