Not compatible with lodash 4.17

[trystian1]

Geppetto cannot be used with lodash 4.17.
Since lodash dropped support for binding this to their functions

         _.each(wiring.values, function(value, key) {
                this.wireValue(key, value);
            }, this)

should be

_.each(wiring.values, (value, key) => {
          this.wireValue(key, value);
});

[trystian1]

This should fix it:
#93