Add option to use returnDocument

The `mongodb` Node.js driver deprecated use of `returnOriginal` in
favour of `returnDocument` in [v3.6][1].

This non-breaking change allows consumers to opt in to using the newer
`returnDocument` by setting an option on construction

```js
var queue = mongoDbQueue(db, 'queue', { returnDocument : true })
```

[1]: mongodb/node-mongodb-native#2808

README.md

@@ -237,6 +237,18 @@ msg = {
 Notice that the payload from the `deadQueue` is exactly the same as the original message
 when it was on the original queue (except with the number of tries set to 5).
 
+### returnDocument ###
+
+The `mongodb` Node.js driver [deprecated](https://github.com/mongodb/node-mongodb-native/pull/2808)
+use of `returnOriginal` in favor of `returnDocument` when using `findOneAndUpdate()`.
+
+If you want to opt in to using the newer `returnDocument`, set the `returnDocument` option
+to `true`:
+
+```
+var queue = mongoDbQueue(db, 'queue', { returnDocument : true })
+```
+
 ## Operations ##
 
 ### .add() ###

mongodb-queue.js

@@ -44,6 +44,7 @@ function Queue(db, name, opts) {
     this.col = db.collection(name)
     this.visibility = opts.visibility || 30
     this.delay = opts.delay || 0
+    this.returnDocument = opts.returnDocument
 
     if ( opts.deadQueue ) {
         this.deadQueue = opts.deadQueue
@@ -120,8 +121,11 @@ Queue.prototype.get = function(opts, callback) {
             visible : nowPlusSecs(visibility),
         }
     }
+    var options = self._optionsWithNewDocument({
+        sort: sort
+    })
 
-    self.col.findOneAndUpdate(query, update, { sort: sort, returnOriginal : false }, function(err, result) {
+    self.col.findOneAndUpdate(query, update, options, function(err, result) {
         if (err) return callback(err)
         var msg = result.value
         if (!msg) return callback()
@@ -175,7 +179,9 @@ Queue.prototype.ping = function(ack, opts, callback) {
             visible : nowPlusSecs(visibility)
         }
     }
-    self.col.findOneAndUpdate(query, update, { returnOriginal : false }, function(err, msg, blah) {
+    var options = self._optionsWithNewDocument({})
+
+    self.col.findOneAndUpdate(query, update, options, function(err, msg, blah) {
         if (err) return callback(err)
         if ( !msg.value ) {
             return callback(new Error("Queue.ping(): Unidentified ack  : " + ack))
@@ -197,7 +203,8 @@ Queue.prototype.ack = function(ack, callback) {
             deleted : now(),
         }
     }
-    self.col.findOneAndUpdate(query, update, { returnOriginal : false }, function(err, msg, blah) {
+    var options = self._optionsWithNewDocument({})
+    self.col.findOneAndUpdate(query, update, options, function(err, msg, blah) {
         if (err) return callback(err)
         if ( !msg.value ) {
             return callback(new Error("Queue.ack(): Unidentified ack : " + ack))
@@ -266,3 +273,12 @@ Queue.prototype.done = function(callback) {
         callback(null, count)
     })
 }
+
+Queue.prototype._optionsWithNewDocument = function(query) {
+    if (this.returnDocument) {
+        query.returnDocument = 'after'
+    } else {
+        query.returnOriginal = false
+    }
+    return query
+}