convex lisp: update doesn't apply all arguments

Tested with Convex **0.8.2**

`update` doesn't apply arguments correctlly.

With two arguments it is fine
```clojure
(update {:a 0} :a + 1) ;=> 1
```

With more than two arguments it fails to apply the second argument
```clojure
(update {:a 0} :a + 1 2) ;=> 2, incorrect, should be 3
(update {:a 0} :a + 1 2 3) ;=> 5, should be 6
(update {:a 0} :a + 1 2 3 4) ;=> 9, should be 10
```