parser: Use strings.Contains instead of strings.Index
parser: Use strings.Contains instead of strings.Index

Closes #2400

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