Fix typo in reset_mode

Can double-check there:
<https://www.w3.org/TR/2014/CR-html5-20140204/syntax.html#the-insertion-mode>.

src/html_parser.ml

@@ -1121,7 +1121,7 @@ let parse requested_context report (tokens, set_tokenizer_state, set_foreign) =
           | _::ancestors -> iterate' ancestors
         in
         iterate' ancestors
-      | {element_name = _, ("tr" | "th")}::_::_ -> in_cell_mode
+      | {element_name = _, ("td" | "th")}::_::_ -> in_cell_mode
       | {element_name = _, "tr"}::_ -> in_row_mode
       | {element_name = _, ("tbody" | "thead" | "tfoot")}::_ ->
         in_table_body_mode