icu: Update source URL.
icu: Update source URL.

The old one resulted in an HTML page for me rather than the .tgz file.

juergenpf/MSYS2-packages,JPeterMugaas/MSYS2-packages,juergenpf/MSYS2-packages,Alexpux/MSYS2-packages,juergenpf/MSYS2-packages,atom2013/MSYS2-packages,mati865/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,waterlan/MSYS2-packages,waterlan/MSYS2-packages,atom2013/MSYS2-packages,mati865/MSYS2-packages,atom2013/MSYS2-packages,atom2013/MSYS2-packages,waterlan/MSYS2-packages,JPeterMugaas/MSYS2-packages,waterlan/MSYS2-packages,juergenpf/MSYS2-packages,Alexpux/MSYS2-packages,Alexpux/MSYS2-packages,juergenpf/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,Alexpux/MSYS2-packages