fix: removed depreciation warnings

lib/index.js

@@ -1,4 +1,5 @@
 let util = require('./util')
+var MongoClient = require('mongodb').MongoClient
 let monk = require('monk')
 let debug = require('debug')
 
@@ -87,3 +88,42 @@ let models = function(path) {
   })
   return models
 }
+
+monk.manager.prototype.open = function (uri, opts, fn) {
+  /*
+   * Monkey patch to remove db event listener warnings
+   * @todo remove when monk is removed
+   * @see https://www.mongodb.com/community/forums/t/node-44612-deprecationwarning-listening-to-events-on-
+       the-db-class-has-been-deprecated-and-will-be-removed-in-the-next-major-version/15849/4
+   */
+  var STATE = {
+    CLOSED: 'closed',
+    OPENING: 'opening',
+    OPEN: 'open'
+  }
+  MongoClient.connect(uri, opts, function (err, client) {
+    // this = Manager
+    if (err) {
+      this._state = STATE.CLOSED
+      this.emit('error-opening', err)
+    } else {
+      this._state = STATE.OPEN
+
+      this._client = client
+      this._db = client.db()
+
+      // set up events
+      var self = this
+      ;['authenticated', 'close', 'error', 'parseError', 'timeout'].forEach(function (eventName) {
+        self._client.on(eventName, function (e) {
+          self.emit(eventName, e)
+        })
+      })
+
+      this.emit('open', this._db)
+    }
+    if (fn) {
+      fn(err, this)
+    }
+  }.bind(this))
+}