Added function to update spreadsheet headers

Author: akskha

python/quip.py

@@ -486,13 +486,12 @@ def update_spreadsheet_headers(self, thread_id, *headers, **kwargs):
             spreadsheet = self.get_named_spreadsheet(kwargs["name"], thread_id)
         else:
             spreadsheet = self.get_first_spreadsheet(thread_id)
-        section_id = self.get_last_row_item_id(spreadsheet)
-        operation = self.AFTER_SECTION
+        section_id = self.get_first_row_item_id(spreadsheet)
         return self.edit_document(
             thread_id=thread_id,
             content=content,
             section_id=section_id,
-            operation=operation)
+            operation=self.PREPEND)
 
     def update_spreadsheet_row(self, thread_id, header, value, updates, **args):
         """Finds the row where the given header column is the given value, and