A bookshelf plugin for performing upserts
npm install bookshelf-upsert> A Bookshelf plugin that adds model.upsert()

```
$ npm install --save bookshelf-upsert
`js
const upsert = require('bookshelf-upsert')
bookshelf.plugin(upsert)
`
`js
const model = require('a-bookshelf-model')
model.forge({ some: 'data' })
.where({ optional: 'constraint' })
.upsert({ optional: 'attributes' })
`
Bookshelf model instances are provided the upsert method, which may be given attributes and options that will be passed along to model.save()`. This implementation of upsert first attempts an update then if no rows are updated it follows up with an insert.
MIT