docs(ngAnimate): staggering example should contain duration:0s property

As of 1.4.4 this property needs to always be in the CSS code

Related angular#12594
Closes angular#12637

Author: matsko

src/ngAnimate/module.js

@@ -188,8 +188,8 @@
  *   /* this will have a 100ms delay between each successive leave animation */
  *   transition-delay: 0.1s;
  *
- *   /* in case the stagger doesn't work then the duration value
- *    must be set to 0 to avoid an accidental CSS inheritance */
+ *   /* As of 1.4.4, this must always be set: it signals ngAnimate
+ *     to not accidentally inherit a delay property from another CSS class */
  *   transition-duration: 0s;
  * }
  * .my-animation.ng-enter.ng-enter-active {