allow customization of exiting class (#389)

Author: miguelcobain

addon/components/flash-message.hbs

@@ -1,5 +1,5 @@
 <div
-  class="flash-message {{this.alertType}} {{if this.exiting "exiting"}} {{if this.active "active"}}"
+  class="flash-message {{this.alertType}} {{if this.exiting this.exitingClass}} {{if this.active "active"}}"
   role="alert"
   ...attributes
   {{on "click" this.onClick}}

addon/components/flash-message.js

@@ -42,6 +42,10 @@ export default class FlashMessage extends Component {
     return this.args.flash.exiting;
   }
 
+  get exitingClass() {
+    return this.args.exitingClass || 'exiting';
+  }
+
   get messageStylePrefix() {
     return this.args.messageStylePrefix ?? this._defaultMessageStylePrefix;
   }