Bump version to 2.1.2

Yotta version bumped to 2.1.3, as we had to do one more patch release to the
yotta registry to accommodate for dependencies updates.
diff --git a/doxygen/input/doc_mainpage.h b/doxygen/input/doc_mainpage.h
index 076f24d..16320da 100644
--- a/doxygen/input/doc_mainpage.h
+++ b/doxygen/input/doc_mainpage.h
@@ -21,7 +21,7 @@
  */
 
 /**
- * @mainpage mbed TLS v2.1.1 source code documentation
+ * @mainpage mbed TLS v2.1.2 source code documentation
  *
  * This documentation describes the internal structure of mbed TLS.  It was
  * automatically generated from specially formatted comment blocks in