Update msys2 to 20200720 (#447)

Author: ifurther

msys2/Dockerfile

@@ -3,7 +3,7 @@ FROM mcr.microsoft.com/windows/servercore:1809 AS builder
 RUN powershell -Command \
     $ProgressPreference = 'SilentlyContinue' ; \
     Write-Output 'Downloading msys2' ; \
-    curl.exe -o msys2.tar.xy http://repo.msys2.org/distrib/x86_64/msys2-base-x86_64-20181211.tar.xz ; \
+    curl.exe -o msys2.tar.xy http://repo.msys2.org/distrib/x86_64/msys2-base-x86_64-20200720.tar.xz ; \
     Install-Package -Scope CurrentUser -Force 7Zip4Powershell ; \
     Write-Output 'Extracting tar.xz' ; \
     Expand-7zip msys2.tar.xy . ; \