fix(example): correct markup in the hello world example

Author: pkozlowski-opensource

modules/examples/src/hello_world/app.js

@@ -20,7 +20,7 @@ import {bootstrap, Component, Decorator, TemplateConfig, NgElement} from 'core/c
  // The template for the component.
  // Expressions in the template (like {{greeting}}) are evaluated in the
  // context of the HelloCmp class below.
- inline: `{{greeting}} <span red>world</foo>!`,
+ inline: `{{greeting}} <span red>world</span>!`,
  // All directives used in the template need to be specified. This allows for
  // modularity (RedDec can only be used in this template)
  // and better tooling (the template can be invalidated if the attribute is