Rewrite TestRSSOutput to use Afero
Rewrite TestRSSOutput to use Afero

When we have a virtual filesystem, we might as well test as close to the iron as possible.

mayah/hugo,mdhender/hugo,fedelibre/hugo,digitalcraftsman/hugo,Zenithar/hugo,anthonyfok/hugo,mayah/hugo,digitalcraftsman/hugo,tubo028/hugo,Zenithar/hugo,mdhender/hugo,jygastaud/hugo,gohugoio/hugo,mdhender/hugo,MarkDBlackwell/hugo,gohugoio/hugo,bogem/hugo,tubo028/hugo,fedelibre/hugo,gohugoio/hugo,fedelibre/hugo,anthonyfok/hugo,mitchchn/hugo,mdhender/hugo,jygastaud/hugo,anthonyfok/hugo,bogem/hugo,mitchchn/hugo,MarkDBlackwell/hugo,fedelibre/hugo