Bump version to Mbed TLS 2.16.4
diff --git a/doxygen/input/doc_mainpage.h b/doxygen/input/doc_mainpage.h
index a6126f3..de43cdf 100644
--- a/doxygen/input/doc_mainpage.h
+++ b/doxygen/input/doc_mainpage.h
@@ -24,7 +24,7 @@
  */
 
 /**
- * @mainpage mbed TLS v2.16.3 source code documentation
+ * @mainpage mbed TLS v2.16.4 source code documentation
  *
  * This documentation describes the internal structure of mbed TLS.  It was
  * automatically generated from specially formatted comment blocks in