feat(Update): add the ability to specify a pipeline to an update command (#2017)

* feat(Update): add the ability to specify a pipeline to an update command

NODE-1920

Author: Sam Pal

lib/collection.js

@@ -697,7 +697,15 @@ Collection.prototype.updateOne = function(filter, update, options, callback) {
   if (typeof options === 'function') (callback = options), (options = {});
   options = options || {};
 
-  const err = checkForAtomicOperators(update);
+  let err;
+  if (Array.isArray(update)) {
+    for (let i = 0; !err && i < update.length; i++) {
+      err = checkForAtomicOperators(update[i]);
+    }
+  } else {
+    err = checkForAtomicOperators(update);
+  }
+
   if (err) {
     if (typeof callback === 'function') return callback(err);
     return this.s.promiseLibrary.reject(err);