Use correct opcode count

Code comment contains an off-by-one error, update it to the correct
value '61'.

src/blockdata/opcodes.rs

@@ -830,7 +830,7 @@ macro_rules! ordinary_opcode {
     );
 }
 
-// "Ordinary" opcodes -- should be 60 of these
+// "Ordinary" opcodes -- should be 61 of these
 ordinary_opcode! {
     // pushdata
     OP_PUSHDATA1, OP_PUSHDATA2, OP_PUSHDATA4,