tools/pyboard.py: Make -c (inline Python code) option compatible with python2.

tools/pyboard.py

@@ -275,7 +275,7 @@ def main():
             sys.exit(1)
 
     if args.command is not None:
-        execbuffer(bytes(args.command, 'utf-8'))
+        execbuffer(args.command.encode('utf-8'))
 
     for filename in args.files:
         with open(filename, 'rb') as f: