output: Fix output format mixup in example
output: Fix output format mixup in example

See #3481

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