Fix for Loading a Previously Serialized Index

[DannyNemer]

See issue #18

As demonstrated below, when loading a serialized index, lunr.js incorrectly loads the serialized index's documentStore.

First, create an index, add a document to the index, and log the index.documentStore.store to show its correct form:

var index = lunr(function () { //create index
    this.field('title')
    this.ref('id')
})
index.add({id: 100, title: 'apple' }) //add document to index
console.log(index.documentStore.store) //log documentStore.store before serializing index

The following is the log of the index.documentStore.store in its correct form:

{ '100': { length: 1, elements: [ 'appl' ] } }

Then, serialize the index and store it to the database:

user.index = index.toJSON() //serialize index and store it in the database
user.save() //save changes to database

Load the serialized index and log the index.documentStore.store to show it in its incorrect form:

index = lunr.Index.load(user.index) //load previously serialized index from database
console.log(index.documentStore.store) //log incorrect documentStore after loading serialized index

The following is the log of the index.documentStore.store in its incorrect form:

{ '100': { length: 1, elements: { length: 1, elements: [Object] } } }

Bug: The bug occurs on line 962 of lunr.js in the lunr.Store.load() function, which is called in lunr.Index.load(). Simply, this is fixed by changing

memo[key] = lunr.SortedSet.load(serialisedData.store[key])

to

memo[key] = lunr.SortedSet.load(serialisedData.store[key].elements)