Added DeliveryModes.EPHEMERAL (#1058)

Author: tracyboehrer

libraries/bot-schema/src/main/java/com/microsoft/bot/schema/Activity.java

@@ -1000,7 +1000,7 @@ public void setImportance(String withImportance) {
      * A delivery hint to signal to the recipient alternate delivery paths for the
      * activity.
      * <p>
-     * The default delivery mode is \"default\".
+     * The default delivery mode is \"default\".  See {@link DeliveryModes}.
      *
      * @return The delivery mode hint.
      */

libraries/bot-schema/src/main/java/com/microsoft/bot/schema/DeliveryModes.java

@@ -23,7 +23,12 @@ public enum DeliveryModes {
     /**
      * The value for expected replies delivery modes.
      */
-    EXPECT_REPLIES("expectReplies");
+    EXPECT_REPLIES("expectReplies"),
+
+    /**
+     * The value for ephemeral delivery modes.
+     */
+    EPHEMERAL("ephemeral");
 
     /**
      * The actual serialized value for a DeliveryModes instance.