[appveyor] update configuration to support cache (#1559)

build/appveyor-msys2-upgrade.bash

@@ -1,10 +0,0 @@
-set -e -x
-
-base_url='http://repo.msys2.org/msys/x86_64/'
-packages="libzstd-1.4.4-2-x86_64.pkg.tar.xz pacman-5.2.1-6-x86_64.pkg.tar.xz zstd-1.4.4-2-x86_64.pkg.tar.xz"
-for p in $packages
-do
-    curl "${base_url}$p" -o "$p"
-done
-pacman -U --noconfirm $packages
-rm -f $packages