Slug is not working as expected

In cljs:  
```clojure
(slug "fööbar") ;; -> foobar
(slug "FÖÖBAR") ;; -> fbar
```
In clj:
```clojure
(slug "fööbar") ;; -> foobar
(slug "FÖÖBAR") ;; -> foobar
```  

The issue seems to be, that `strip-accents` only strips lower-case accents and that the string can still contain uppercase letters at this point.