Fix version number in doxygen

Signed-off-by: Martin Melik-Merkumians <melik-merkumians@acin.tuwien.ac.at>

source/opener.doxyfile

@@ -38,7 +38,7 @@ PROJECT_NAME           = "OpENer - Open Source EtherNet/IP(TM)  I/O Target Stack
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 2.1
+PROJECT_NUMBER         = 2.2
 
 # 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