docs: Update documentation for the release of ndnSIM 2.3

Change-Id: I3d23bcf29f4858049d1040a3e421e1c7151b3ee1
Refs: #3876
diff --git a/docs/ns3_html_theme/ns3_doxy_header.html b/docs/ns3_html_theme/ns3_doxy_header.html
index a63e509..5f45f4f 100644
--- a/docs/ns3_html_theme/ns3_doxy_header.html
+++ b/docs/ns3_html_theme/ns3_doxy_header.html
@@ -33,7 +33,7 @@
   </td>
   <td id="projecttext">
    <div id="projectbrief">NS-3 based Named Data Networking (NDN) simulator</div>
-   <span id="projectnumber">ndnSIM 2.0: NDN, CCN, CCNx, content centric networks</span>
+   <span id="projectnumber">ndnSIM 2.3: NDN, CCN, CCNx, content centric networks</span>
   </td>
   <!--BEGIN DISABLE_INDEX-->
    <!--BEGIN SEARCHENGINE-->