Fix plotpanel matplotlib requirement
Fix plotpanel matplotlib requirement

SasView/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,SasView/sasview,SasView/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview,SasView/sasview