reduce (cb, initialValue) {
    const data = this.getAll()
    return data.reduce(cb, initialValue)
  }
Reduce the data in the collection to a single value and return the result.

@example
const totalVotes = collection.reduce((prev, record) => {
  return prev + record.upVotes + record.downVotes;
}, 0);

@method Collection#reduce
@since 3.0.0
@param {Function} cb Reduction callback.
@param {*} initialValue Initial value of the reduction.
@returns {*} The result.