:+1: version and update docs

CHANGES.md

@@ -1,7 +1,7 @@
 CHANGES
 ========
 
-## 2.3.9-RC
+## 2.4.0-RC
 
 * Feature: Support Footnotes
 * Feature: Support Task lists

package.json

@@ -1,6 +1,6 @@
 {
   "name": "crowi-plus",
-  "version": "2.3.9-RC",
+  "version": "2.4.0-RC",
   "description": "Enhanced Crowi",
   "tags": [
     "wiki",