Change default prod-mode missing translation logging level

Changed from :error to :debug.

This is a more sensible default since the recent changes that allow
more graceful locale fallback; particularly when using the Ring
middleware.

src/taoensso/tower.clj

@@ -46,7 +46,7 @@
          (fn [{:keys [dev-mode? locale k-or-ks]}]
            (if dev-mode?
              (timbre/warn  "Missing translation" k-or-ks "for" locale)
-             (timbre/error "Missing translation" k-or-ks "for" locale)))}))
+             (timbre/debug "Missing translation" k-or-ks "for" locale)))}))
 
 (defn set-config! [[k & ks] val] (swap! config assoc-in (cons k ks) val))