Fix #784 by adding the gson adapter (#808)

Author: seratch

bolt-socket-mode/src/test/java/samples/SimpleApp.java

@@ -4,6 +4,8 @@
 import com.slack.api.bolt.AppConfig;
 import com.slack.api.bolt.socket_mode.SocketModeApp;
 import com.slack.api.model.event.AppMentionEvent;
+import com.slack.api.model.event.MessageChangedEvent;
+import com.slack.api.model.event.MessageDeletedEvent;
 import com.slack.api.model.event.MessageEvent;
 import config.Constants;
 
@@ -42,6 +44,9 @@ public static void main(String[] args) throws Exception {
             return ctx.ack();
         });
 
+        app.event(MessageChangedEvent.class, (req, ctx) -> ctx.ack());
+        app.event(MessageDeletedEvent.class, (req, ctx) -> ctx.ack());
+
         app.globalShortcut("socket-mode-global-shortcut", (req, ctx) -> {
             ctx.asyncClient().viewsOpen(r -> r
                     .triggerId(req.getContext().getTriggerId())

slack-api-client/src/main/java/com/slack/api/util/json/GsonFactory.java

@@ -33,6 +33,7 @@ public static Gson createSnakeCase() {
                 .registerTypeAdapter(RichTextElement.class, new GsonRichTextElementFactory())
                 .registerTypeAdapter(LogsResponse.DetailsChangedValue.class, new GsonAuditLogsDetailsChangedValueFactory())
                 .registerTypeAdapter(Attachment.VideoHtml.class, new GsonMessageAttachmentVideoHtmlFactory())
+                .registerTypeAdapter(MessageChangedEvent.PreviousMessage.class, new GsonMessageChangedEventPreviousMessageFactory())
                 .create();
     }