docs(Angular): fix punctuation

Closes angular#10481

src/Angular.js

@@ -1176,7 +1176,7 @@ function getNgAttribute(element, ngAttr) {
  * document would not be compiled, the `AppController` would not be instantiated and the `{{ a+b }}`
  * would not be resolved to `3`.
  *
- * `ngApp` is the easiest, and most common, way to bootstrap an application.
+ * `ngApp` is the easiest, and most common way to bootstrap an application.
  *
  <example module="ngAppDemo">
    <file name="index.html">