Updated to angular 11

Now compiling with strict mode in typescript
Need to error checking now

bookie/src/app/guest-book/guest-book-list.ts

@@ -3,4 +3,10 @@ import { GuestBook } from './guest-book';
 export class GuestBookList {
   date: string;
   list: GuestBook[];
+
+  public constructor(init?: Partial<GuestBookList>) {
+    this.date = '';
+    this.list = [];
+    Object.assign(this, init);
+  }
 }