Short flags throw error

Tested with the following program pieced together from the README:

```clojure
(load "git@github.com:carpentry-org/clig@main")

(def p (Clig.new @"my-program" @"doesn't do anything interesting"))

(def my-bool-flag (Clig.bool-flag @"force"
(Maybe.Just @"b")
@"false"
@"abandon all safety"))
(def my-int-flag (Clig.int-flag @"count"
(Maybe.Nothing)
@"1"
@"repeat n times"))

(defn main []
(do (Clig.add-flag &p &my-bool-flag)
(Clig.add-flag &p &my-int-flag)
(match (Clig.parse &p true)
(Result.Error err) (IO.println &(str err))
(Result.Success _)
(IO.println "hi")
)))
```

Unfortunately, when trying to provide the program with the short flag `b`, I get the following output:
```
unknown flag force
```

This seems to only happen with short flags.

Cheers