fix small doc error.
fix small doc error.

caskdata/coopr,cdapio/coopr,caskdata/coopr,cdapio/coopr,quantiply-fork/coopr,quantiply-fork/coopr,cdapio/coopr,caskdata/coopr,caskdata/coopr,cdapio/coopr,quantiply-fork/coopr,caskdata/coopr,cdapio/coopr,quantiply-fork/coopr