fix configure.py help string for argparse compatibility

Author: pongo1231

configure.py

@@ -29,7 +29,7 @@ def make_objdir_name(p):
                        help='Enable optimization')
 parser.options.add_argument('-s', '--sdks', default='all', dest='sdks',
                        help='Build against specified SDKs; valid args are "all", "present", or '
-                            'comma-delimited list of engine names (default: %default)')
+                            'comma-delimited list of engine names (default: %(default)s)')
 parser.options.add_argument('--enable-tests', default=False, dest='enable_tests', action='store_true',
                        help='Build tests.')
 parser.Configure()