[Zlib] Issue with version override.

[jamespack]

Downloading zlib128.zip
Failed to download zlib128.zip.
If you are using a proxy, please ensure your proxy settings are correct.
Possible causes are:

1. You are actually using an HTTP proxy, but setting HTTPS_PROXY variable to https//address:port.
   This is not correct, because https:// prefix claims the proxy is an HTTPS proxy, while your proxy (v2ray, shadowsocksr, etc...) is an HTTP proxy.
   Try setting http://address:port to both HTTP_PROXY and HTTPS_PROXY instead.
2. If you are using Windows, vcpkg will automatically use your Windows IE Proxy Settings set by your proxy software. See, If HTTP(S)_PROXY already exist in environment variable, do not use IE Proxy (#49) vcpkg-tool#77
   The value set by your proxy might be wrong, or have same https:// prefix issue.
3. Your proxy's remote server is our of service.
   If you've tried directly download the link, and believe this is not a temporay download server failure, please submit an issue at https://github.com/Microsoft/vcpkg/issues
   to report this upstream download server failure.
   error: zlib port link generated: failed: status code 404
   CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:231 (message):
   Download failed, halting portfile.
   Call Stack (most recent call first):
   C:/Users/james/AppData/Local/vcpkg/registries/git-trees/3309ec82cd96d752ff890c441cb20ef49b52bf94/portfile.cmake:3 (vcpkg_download_distfile)
   scripts/ports.cmake:196 (include)