Work around MSYS2 update issue (msys2/MSYS2-packages#1141)

Author: Mitsutoshi Aoe

appveyor.yml

@@ -12,7 +12,7 @@ install:
 - curl -ostack.zip -LsS --insecure https://www.stackage.org/stack/windows-x86_64
 - 7z x stack.zip stack.exe
 - stack setup > nul
-- stack exec -- pacman --noconfirm --needed -Sy bash pacman pacman-mirrors msys2-runtime msys2-runtime-devel
+- stack exec -- pacman --noconfirm --needed --ask 20 -Sy bash pacman pacman-mirrors msys2-runtime msys2-runtime-devel
 - stack exec -- pacman --noconfirm -Syu
 - stack exec -- pacman --noconfirm -Syuu
 - stack exec -- pacman --noconfirm -S base-devel mingw-w64-x86_64-pkg-config mingw-w64-x86_64-toolchain mingw-w64-x86_64-gtk2