Update appveyor config
Update appveyor config

Remove "image" setting as the "WMF 5" image is deprecated.

Fixes #3061, #3142

mdhender/hugo,mdhender/hugo,anthonyfok/hugo,anthonyfok/hugo,fedelibre/hugo,fedelibre/hugo,gohugoio/hugo,digitalcraftsman/hugo,gohugoio/hugo,digitalcraftsman/hugo,mitchchn/hugo,fedelibre/hugo,mitchchn/hugo,fedelibre/hugo,gohugoio/hugo,mdhender/hugo,anthonyfok/hugo,mdhender/hugo