Fix exception syntax

Author: Snigelson

stm32loader.py

@@ -383,7 +383,7 @@ def usage():
 
     try:
         opts, args = getopt.getopt(sys.argv[1:], "hqVewvrp:b:a:l:g:")
-    except getopt.GetoptError, err:
+    except getopt.GetoptError as err:
         # print help information and exit:
         print (str(err)) # will print something like "option -a not recognized"
         usage()