switch appveyor to cygwin over https

.appveyor.yml

@@ -30,7 +30,7 @@ init:
   - git config --global core.autocrlf input
 
 install:
-  - ps: if (Test-Path Env:\CYG_ROOT) { Start-FileDownload "http://cygwin.com/$env:CYG_SETUP" -FileName "$env:CYG_SETUP" }
+  - ps: if (Test-Path Env:\CYG_ROOT) { Start-FileDownload "https://cygwin.com/$env:CYG_SETUP" -FileName "$env:CYG_SETUP" }
   - if defined CYG_ROOT (%CYG_SETUP% --quiet-mode --no-shortcuts --only-site --root "%CYG_ROOT%" --site "%CYG_MIRROR%" --local-package-dir "%CYG_CACHE%" --packages "%CYG_PACKAGES%" --upgrade-also)
   - if defined MSYSTEM (%BASH% -lc "pacman -Suuy --noconfirm")
   # the following line is not a duplicate line: