Update Doxygen version

Change-Id: I8718a128ea4297fe8acf9fabac9cf3a6dc4c6c70
Signed-off-by: Giuseppe Rossini <giuseppe.rossini@arm.com>
diff --git a/docs/Doxyfile b/docs/Doxyfile
index 7f5aa5b..9a1eb17 100644
--- a/docs/Doxyfile
+++ b/docs/Doxyfile
@@ -38,7 +38,7 @@
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.0
+PROJECT_NUMBER         = 20.02
 
 # 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