Fix to python version critical log message

src/bitmessagemain.py

@@ -40,7 +40,7 @@ from debug import logger
 import sys
 if sys.platform == 'darwin':
     if float("{1}.{2}".format(*sys.version_info)) < 7.5:
-        logger.critical("You should use python 2.7.5 or greater. Your version: %s", format(*sys.version_info))
+        logger.critical("You should use python 2.7.5 or greater. Your version: %s", "{0}.{1}.{2}".format(*sys.version_info))
         sys.exit(0)
 
 def connectToStream(streamNumber):