Currently rST depends on old version sphinx-2.x.
Install it by downloading it.

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
---
 .cirrus.yml | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/.cirrus.yml b/.cirrus.yml
index d1fe63b343..599fd299e3 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -110,6 +110,11 @@ windows_msys2_task:
           mingw-w64-x86_64-curl \
           mingw-w64-x86_64-gnutls \
           "
+        bitsadmin /transfer msys_download /dynamic /download /priority FOREGROUND `
+          https://repo.msys2.org/mingw/x86_64/mingw-w64-x86_64-python-sphinx-2.3.1-1-any.pkg.tar.xz `
+          C:\tools\mingw-w64-x86_64-python-sphinx-2.3.1-1-any.pkg.tar.xz
+        C:\tools\msys64\usr\bin\bash.exe -lc "pacman --noconfirm -U /c/tools/mingw-w64-x86_64-python-sphinx-2.3.1-1-any.pkg.tar.xz"
+        del C:\tools\mingw-w64-x86_64-python-sphinx-2.3.1-1-any.pkg.tar.xz
         C:\tools\msys64\usr\bin\bash.exe -lc "rm -rf /var/cache/pacman/pkg/*"
         cd C:\tools\msys64
         echo "Start archive"
-- 
2.28.0.windows.1