Keep the order of header fields

piplicenses.py

@@ -253,7 +253,7 @@ def get_string(self, **kwargs):
         return json.dumps(lines, indent=2, sort_keys=True)
 
 
-class CSVPrettyTable(JsonPrettyTable):
+class CSVPrettyTable(PrettyTable):
     """PrettyTable-like class exporting to CSV"""
 
     def get_string(self, **kwargs):
@@ -275,10 +275,12 @@ def esc_quotes(val):
         formatted_rows = self._format_rows(rows, options)
 
         lines = []
-        for index, row in enumerate(formatted_rows):
-            values = row.values() if index else row.keys()
+        formatted_header = ','.join(['"%s"' % (esc_quotes(val), )
+                                     for val in self._field_names])
+        lines.append(formatted_header)
+        for row in formatted_rows:
             formatted_row = ','.join(['"%s"' % (esc_quotes(val), )
-                                      for val in values])
+                                      for val in row])
             lines.append(formatted_row)
 
         return '\n'.join(lines)

test_piplicenses.py

@@ -325,7 +325,7 @@ def test_format_csv(self):
         output_string = create_output_string(args)
 
         obtained_header = output_string.split('\n', 1)[0]
-        expected_header = '"Version","Name","License","Author"'
+        expected_header = '"Name","Version","License","Author"'
         self.assertEqual(obtained_header, expected_header)
 
     def test_from_compatibility(self):