automation: use newer Windows base image
It looks like the old base image disappeared. Let's use a newer
image that exists today.
Differential Revision: https://phab.mercurial-scm.org/D6671
default = 'changelog'
mimetype = 'text/xml; charset={encoding}'
header = header.tmpl
changelog = changelog.tmpl
changelogentry = changelogentry.tmpl
filelog = filelog.tmpl
filelogentry = filelogentry.tmpl
tags = tags.tmpl
tagentry = tagentry.tmpl
bookmarks = bookmarks.tmpl
bookmarkentry = bookmarkentry.tmpl
branches = branches.tmpl
branchentry = branchentry.tmpl
error = error.tmpl
filedifflink = '{file|escape}<br />'
fileellipses = '{file|escape}<br />'
filenodelink = '{file|escape}<br />'
filenolink = '{file|escape}<br />'