Link to version 2.2x and 2.3.x javadocs

This PR adds links to the version 2.2.x and 2.3.x javadocs.
diff --git a/reference/javadoc/index.md b/reference/javadoc/index.md
index 800bcb3..62f406f 100644
--- a/reference/javadoc/index.md
+++ b/reference/javadoc/index.md
@@ -4,6 +4,8 @@
 permalink: /reference/javadoc/
 ---
 
+* [2.3.x](/reference/javadoc/2.3.x/)
+* [2.2.x](/reference/javadoc/2.2.x/)
 * [2.1.x](/reference/javadoc/2.1.x/)
 * [2.0.x](/reference/javadoc/2.0.x/)
 * [1.9.x](/reference/javadoc/1.9.x/)