Update appveyor.yml

Author: yebai

appveyor.yml

@@ -10,6 +10,8 @@ environment:
     # MINGW_URL: https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win32/Personal%20Builds/mingw-builds/5.3.0/threads-win32/dwarf/i686-5.3.0-release-win32-dwarf-rt_v4-rev0.7z/download
     MINGW_URL: http://mlg.eng.cam.ac.uk/hong/i686-5.3.0-release-win32-dwarf-rt_v4-rev0.7z
     MINGW_ARCHIVE: i686-5.3.0-release-win32-dwarf-rt_v4-rev0.7z
+      allow_failures: # Cairo.jl doesn't build on Win32; remove this when Cairo has a new release.
+      - MINGW_DIR: mingw32
 
 notifications:
   - provider: Email