Bump version to Mbed TLS 2.7.18

Executed ./scripts/bump_version.sh --version 2.7.18

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/doxygen/input/doc_mainpage.h b/doxygen/input/doc_mainpage.h
index 7f7185a..7f01663 100644
--- a/doxygen/input/doc_mainpage.h
+++ b/doxygen/input/doc_mainpage.h
@@ -49,7 +49,7 @@
  */
 
 /**
- * @mainpage mbed TLS v2.7.17 source code documentation
+ * @mainpage mbed TLS v2.7.18 source code documentation
  *
  * This documentation describes the internal structure of mbed TLS.  It was
  * automatically generated from specially formatted comment blocks in