Upgrade bson to 4.x (latest)

lib/utils.js

@@ -624,6 +624,12 @@ function createPromiseCallback() {
   return cb;
 }
 
+function isBsonType(value) {
+  // bson@1.x stores _bsontype on ObjectID instance, bson@4.x on prototype
+  return value.hasOwnProperty('_bsontype') ||
+    value.constructor.prototype.hasOwnProperty('_bsontype');
+}
+
 /**
  * Dedupe an array
  * @param {Array} an array
@@ -636,7 +642,7 @@ function uniq(a) {
   }
   assert(Array.isArray(a), 'array argument is required');
   var comparableA = a.map(
-    item => item.hasOwnProperty('_bsontype') ? item.toString() : item
+    item => isBsonType(item) ? item.toString() : item
   );
   for (var i = 0, n = comparableA.length; i < n; i++) {
     if (comparableA.indexOf(comparableA[i]) === i) {

package.json

@@ -36,7 +36,7 @@
   "devDependencies": {
     "@types/node": "^10.0.8",
     "async-iterators": "^0.2.2",
-    "bson": "^1.0.4",
+    "bson": "^4.0.1",
     "coveralls": "^3.0.1",
     "eslint": "^5.1.0",
     "eslint-config-loopback": "^11.0.0",