Use is to compare types

This is consistent with other similar checks in the code base.

Author: DimitriPapadopoulos

tabulate/__init__.py

@@ -124,13 +124,11 @@ def _is_separating_line_value(value):
 
 def _is_separating_line(row):
     row_type = type(row)
-    is_sl = (row_type == list or row_type == str) and (
+    return (row_type is list or row_type is str) and (
         (len(row) >= 1 and _is_separating_line_value(row[0]))
         or (len(row) >= 2 and _is_separating_line_value(row[1]))
     )
 
-    return is_sl
-
 
 def _pipe_segment_with_colons(align, colwidth):
     """Return a segment of a horizontal line with optional colons which