Bump NQP_REVISION.

* Gets complete JVM support for the streaming decode API, which gets
  synchronous sockets back to passing all of their tests after the
  recent refactors.
* Brings in MoarVM changes that mean libuv is no longer used for
  synchronous sockets. This in turn means that the exceptions and
  crashes when trying to use handles across different threads are
  now cleared up (for example, accepting a handle on one thread and
  handing it off to another to communicate).

tools/build/NQP_REVISION

@@ -1 +1 @@
-2017.05
+2017.05-23-g6f0b5b4