code: function _deepKeys(obj, prefix = null) {
    return Object.keys(obj).reduce(function(acc, key){
      var value = obj[key];
  
      if (_isObject(value)) {
        acc.push.apply(acc, _deepKeys(value, prefix ? prefix + '.' + key : key));
      } else {
        acc.push(prefix ? prefix + '.' + key : key);
      }
  
      return acc;
    }, []);
  }
docs: Get all keys for the given object recursively
  
  Ex: { user: { email: 'foo@bar.com', id: 2 } } => ['user.email', 'user.id']