Looks like they've addressed this in their docs:
Due to express 4.x.x changes, we now need to pass express-session to the function connect-redis exports in order to extend express-session.Store:
var session = require('express-session') , RedisStore = require('connect-redis')(session);
app.use(session({ store: new RedisStore(options), secret: 'keyboard cat' }))
https://github.com/visionmedia/connect-redis under usage