Typo in comment.

demos/interpreter/backwards.html

@@ -156,7 +156,7 @@
 
     // Stack of serializations.  Each object contains three properties:
     //   .json: A full serialization of the interpreter's state.
-    //   .delta: Instead of a full serialization, a delta from the next sate.
+    //   .delta: Instead of a full serialization, a delta from the next state.
     //   .highlight: The ID of the block highlighted in this state.
     var serializationStack = [];