I had the same problem when I follow the manual with the latest version of Yomen. There is a typo error in the entity library that you can manually fix to complete the tutorial:
( C:\Users\L\AppData\Roaming\npm\ node_modules\generator-webapp\node_modules\cheerio\node_modules\entities\index.js)
var decode = levels.map(function(l){ return l.normal; }),
decodeStrict = levels.map(function(l){ return l.strict; }),
inverse = levels.map(function(l){ return l.inverse; });
To
var decode = levels.map(function(l){ return l.normal; }),
decodeStrict = levels.map(function(l){ return l.strict; }),
encode = levels.map(function(l){ return l.inverse; });