[AUTO][RELEASE]: Update version number in doxygen

Author: chinglee-iot

docs/doxygen/config.doxyfile

@@ -48,7 +48,7 @@ PROJECT_NAME           = coreMQTT
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = v2.3.1+
+PROJECT_NUMBER         = v2.3.1
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a