make cond's default argument lazy

src/Core/Core.idr

@@ -894,7 +894,7 @@ wrapRef x onClose op
        pure o
 
 export
-cond : List (Lazy Bool, Lazy a) -> a -> a
+cond : List (Lazy Bool, Lazy a) -> Lazy a -> a
 cond [] def = def
 cond ((x, y) :: xs) def = if x then y else cond xs def