Merge pull request #13859 from Snorremd/master

Fix: Change MongooseDocument.set() return type from void to this.
See http://mongoosejs.com/docs/api.html#document_Document-set

Modify doc.set() examples in test file to chain the set method in
order to test the "this" return type.

mongoose/index.d.ts

@@ -1010,9 +1010,9 @@ declare module "mongoose" {
      * @param type optionally specify a type for "on-the-fly" attributes
      * @param options optionally specify options that modify the behavior of the set
      */
-    set(path: string, val: any, options?: Object): void;
-    set(path: string, val: any, type: any, options?: Object): void;
-    set(value: Object): void;
+    set(path: string, val: any, options?: Object): this;
+    set(path: string, val: any, type: any, options?: Object): this;
+    set(value: Object): this;
 
     /**
      * The return value of this method is used in calls to JSON.stringify(doc).

mongoose/mongoose-tests.ts

@@ -449,10 +449,7 @@ doc.populate(function (err, doc) {
   });
 });
 doc.populated('path');
-doc.set('path', 999, {});
-doc.set({
-  path: 999
-});
+doc.set('path', 999, {}).set({ path: 999 });
 doc.toJSON({
   getters: true,
   virtuals: false
@@ -1494,4 +1491,4 @@ const extended: mongoose.Model<extended> = base.discriminator<extended>('extende
 const x = new extended({
   username: 'hi',     // required in baseSchema
   email: 'beddiw',    // required in extededSchema
-});
+});