lightstep-tracer-cpp: mark as broken

needs an update + https://github.com/opentracing/opentracing-cpp

(cherry picked from commit eea21b28356ab7d0f02680b34589846dc45d96f0)

pkgs/development/libraries/lightstep-tracer-cpp/default.nix

···
     license = licenses.mit;
     platforms = platforms.linux;
     maintainers = with maintainers; [ cstrahan ];
+    broken = true; # 2018-02-16
   };
 }