[libsigcplusplus] Correct a doxygen comment.

[Murray Cumming <murrayc src gnome org>]

commit f021edeb33574db95f48467406f9bf57aa2525a9
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 20 09:13:21 2016 +0200

    Correct a doxygen comment.

 sigc++/signal.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/signal.h b/sigc++/signal.h
index 13969ee..6208a70 100644
--- a/sigc++/signal.h
+++ b/sigc++/signal.h
@@ -732,7 +732,7 @@ public:
 
   /** Executes a list of slots using an accumulator of type @e T_accumulator in reverse order.
    * The arguments are passed directly on to the slots.
-   * @param a%1 Argument to be passed on to the slots.
+   * @param a Arguments to be passed on to the slots.
    * @return The return value of the last slot invoked.
    */
   static decltype(auto) emit_reverse(signal_impl* impl, type_trait_take_t<T_arg>... a)