docs(ngAnimate): change "&angular#64" to "@" symbol

Previously, we had problems with code that contained symbols that looked
like jsdoc directives.  This has now been fixed so we can convert these
HTML character codes back to @ signs.

Closes angular#6822
Closes angular#6826

Author: Teddy Wing

src/ngAnimate/animate.js

@@ -106,11 +106,11 @@
  *   -webkit-animation: enter_sequence 1s linear; /* Safari/Chrome */
  *   animation: enter_sequence 1s linear; /* IE10+ and Future Browsers */
  * }
- * &#64-webkit-keyframes enter_sequence {
+ * @-webkit-keyframes enter_sequence {
  *   from { opacity:0; }
  *   to { opacity:1; }
  * }
- * &#64keyframes enter_sequence {
+ * @keyframes enter_sequence {
  *   from { opacity:0; }
  *   to { opacity:1; }
  * }