Replace deprecated commands with new dart commands

Author: robbecker-wf

example/README.md

@@ -1,6 +1,6 @@
 # Serving / Viewing React Dart Examples
 
-1. Run `pub get` in your terminal. 
+1. Run `dart pub get` in your terminal. 
 2. Run `webdev serve example`.
 2. Open Chrome.
 3. Navigate to <http://localhost:8080>