change int to bool for backwards compatiblity with tbp1

Author: shakkar23

text/0000-mvp.md

@@ -68,7 +68,7 @@ Attribute       | Description
 `hold`          | Either a pieces if hold is filled or `null` if hold is empty.
 `queue`         | A list of pieces. Example: `["S", "Z", "O"]`
 `combo`         | The number of consecutive line clears that have been made.
-`back_to_back`  | An integer indicating back to back status.
+`back_to_back`  | A boolean indicating back to back status.
 `board`         | A list of 40 lists of 10 board cells.
 
 A board cell can be either `null` to indicate that it is empty, or a string