Fix exception cause in common.py

Author: cool-RR

rsa/common.py

@@ -49,8 +49,8 @@ def bit_size(num: int) -> int:
 
     try:
         return num.bit_length()
-    except AttributeError as e:
-        raise TypeError('bit_size(num) only supports integers, not %r' % type(num)) from e
+    except AttributeError as ex:
+        raise TypeError('bit_size(num) only supports integers, not %r' % type(num)) from ex
 
 
 def byte_size(number: int) -> int: