existence check on fkValue, fixes #49
query() takes a function similar to other Knex methods:

collection.query(function() {
    this.where("id","=","1")
}).fetch().then(console.log)
Changing argument for dynamic, query function from #45
adding grunt-release
Tweaking foreignKey existence check to disallow null, prepping for 0.2.5
release 0.2.5