Problem: wrong copyright dates in newly added files

Solution: fix them

src/ws_connecter.cpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_connecter.hpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_decoder.cpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_decoder.hpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_encoder.cpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_encoder.hpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_engine.cpp

 /*
-Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
 This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_listener.cpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_listener.hpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.
 

src/ws_protocol.hpp

 /*
-    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+    Copyright (c) 2007-2019 Contributors as noted in the AUTHORS file
 
     This file is part of libzmq, the ZeroMQ core engine in C++.