add todo and remove a newline

src/engine/blocks.js

@@ -569,6 +569,7 @@ class Blocks {
                 }
                 // The selected item in the sensing of block menu needs to change based on the
                 // selected target.  Set it to the first item in the menu list.
+                // TODO: https://github.com/LLK/scratch-vm/issues/1787
                 if (block.opcode === 'sensing_of_object_menu') {
                     if (block.fields.OBJECT.value === '_stage_') {
                         this._blocks[block.parent].fields.PROPERTY.value = 'backdrop #';