add missing detail namespace (#2107)

Co-authored-by: Walter Gray <walter.gray@getcruise.com>
diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index 14c63e7..7b58f4e 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -287,7 +287,7 @@
   // C++11 generic lambda for format()
   template <typename FormatContext> struct format_each {
     template <typename T> void operator()(const T& v) {
-      if (i > 0) out = write_delimiter(out);
+      if (i > 0) out = detail::write_delimiter(out);
       out = detail::write_range_entry<Char>(out, v);
       ++i;
     }