Fix stable_async_op_base javadoc

CHANGELOG.md

@@ -1,6 +1,7 @@
 Version 210:
 
 * Tidy up read implementation
+* Fix stable_async_op_base javadoc
 
 --------------------------------------------------------------------------------
 

include/boost/beast/core/async_op_base.hpp

@@ -586,8 +586,8 @@ public:
 #if BOOST_BEAST_DOXYGEN
     template<class Handler>
     stable_async_op_base(
-        Executor1 const& ex1,
         Handler&& handler,
+        Executor1 const& ex1,
         Allocator const& alloc = Allocator());
 #else
     template<