fix whitespace error

Author: Aman Sharma

pandas/core/reshape/concat.py

@@ -17,8 +17,8 @@
 import numpy as np
 
 from pandas._libs import lib
-from pandas.util._exceptions import find_stack_level
 from pandas.util._decorators import set_module
+from pandas.util._exceptions import find_stack_level
 
 from pandas.core.dtypes.common import (
     is_bool,