don't rewrite `~ @` to `~@`

The basic issue is that `~ @a` is being reformatted to `~@a`, which is not semantically equivalent. My guess is that most would choose to write `~(deref a)` instead. This works fine, however `(zprint-str '~(clojure.core/deref a))` prints `~@a`, which might be the most likely manifestation of this bug in practice. An alternative approach might be to not delete the space between the `~ @` in the first place. LMK if you'd rather do that.