Replace {} with ()

This is because g++ (Debian 4.9.1-14) produced an error:

    internal compiler error: in convert_move, at expr.c:331

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=761529 and
#22

apf/apf/misc.h

@@ -98,8 +98,8 @@ class BlockParameter
     /// Constructor. Any arguments are forwarded to both old and current value.
     template<typename... Args>
     explicit BlockParameter(Args&&... args)
-      : _current{args...}
-      , _old{std::forward<Args>(args)...}
+      : _current(args...)
+      , _old(std::forward<Args>(args)...)
     {}
 
     /// Assignment operator.