docs: Fix punctuation for better consistency (angular#50560)

This is to fix a punctuation issue on the "Tour of Heroes - Introduction" page for better consistency.
PR Close angular#50560

aio/content/tutorial/tour-of-heroes/index.md

@@ -18,7 +18,7 @@ You can edit the application in StackBlitz and see the results in real time.
 This *Tour of Heroes* tutorial provides an introduction to the fundamentals of Angular and shows you how to:
 
 * Set up your local Angular development environment.
-* Use the [Angular CLI](cli "CLI command reference") to develop an application
+* Use the [Angular CLI](cli "CLI command reference") to develop an application.
 
 The *Tour of Heroes* application that you build helps a staffing agency manage its stable of heroes.
 The application has many of the features that you'd expect to find in any data-driven application.