[ogdf] Update source link

[LilyWangL]

Fix build error:

.\vcpkg.exe install ogdf
The following packages will be built and installed:
    ogdf[core]:x86-windows
Starting package 1/1: ogdf:x86-windows
Building package ogdf[core]:x86-windows...
-- Downloading http://www.ogdf.net/lib/exe/fetch.php/tech%3aogdf-snapshot-2018-03-28.zip...
-- Downloading http://www.ogdf.net/lib/exe/fetch.php/tech%3aogdf-snapshot-2018-03-28.zip... Failed. Status: 6;"Couldn't resolve host name"
CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:172 (message):

      Failed to download file.
      If you use a proxy, please set the HTTPS_PROXY and HTTP_PROXY environment
      variables to "https://user:password@your-proxy-ip-address:port/".
      Otherwise, please submit an issue at https://github.com/Microsoft/vcpkg/issues

Call Stack (most recent call first):
  ports/ogdf/portfile.cmake:3 (vcpkg_download_distfile)
  scripts/ports.cmake:85 (include)

Related issue: #7841