Correct syntax error

The question feels odd using the `What` question word and the
following paragraph fits better with the `Why` question word.

Author: csralvall

09_5_Scripting_a_P2WPKH.md

@@ -96,7 +96,7 @@ script                                   |                                   sta
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 Bitcoin Scripts are considered successful if there's something in the Stack, and it's non-zero, so SegWit scripts automatically succeed on old nodes as long as the `scriptPubKey` is correctly created with a non-zero pub-key hash. This is called an "anyone-can-spend" transaction, because old nodes verified them as correct without any need for signatures.
 
-> :book: ***What can't old nodes steal SegWit UTXOs?*** SegWit was enabled on the Bitcoin network when 95% of miners signalled that they were ready to start using it. That means that only 5% of nodes at that point might have registered anyone-can-spend SegWit transactions as valid without going through the proper work of checking the `txinwitness`. If they incorrectly incorporated an invalid anyone-can-spend UTXO into a block, the other 95% of nodes would refuse to validate that block, and so it would quickly be orphaned rather than being added to the "main" blockchain. (Certainly, 51% of nodes could choose to stop interpreting SegWit transactions correctly, but 51% of nodes can do anything on a consensus network like a blockchain.)
+> :book: ***Why can't old nodes steal SegWit UTXOs?*** SegWit was enabled on the Bitcoin network when 95% of miners signalled that they were ready to start using it. That means that only 5% of nodes at that point might have registered anyone-can-spend SegWit transactions as valid without going through the proper work of checking the `txinwitness`. If they incorrectly incorporated an invalid anyone-can-spend UTXO into a block, the other 95% of nodes would refuse to validate that block, and so it would quickly be orphaned rather than being added to the "main" blockchain. (Certainly, 51% of nodes could choose to stop interpreting SegWit transactions correctly, but 51% of nodes can do anything on a consensus network like a blockchain.)
 
 Because old nodes always see SegWit scripts as correct, they will always verify them, even without understanding their content.