Bump version to Mbed TLS 2.16.8

Executed "./scripts/bump_version.sh --version 2.16.8"

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/doxygen/input/doc_mainpage.h b/doxygen/input/doc_mainpage.h
index 3faf41a..acd8be1 100644
--- a/doxygen/input/doc_mainpage.h
+++ b/doxygen/input/doc_mainpage.h
@@ -49,7 +49,7 @@
  */
 
 /**
- * @mainpage mbed TLS v2.16.7 source code documentation
+ * @mainpage mbed TLS v2.16.8 source code documentation
  *
  * This documentation describes the internal structure of mbed TLS.  It was
  * automatically generated from specially formatted comment blocks in