Fix references to middleware in docs.
Fix references to middleware in docs.

TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix