contrib: Windows: bump msgpack

Change-Id: I9a2ec38049a3b2e5dcbd04c3ca84e595e69a4e72

contrib/src/msgpack/package.json

 {
     "name": "msgpack-c",
-    "version": "cpp-4.1.3",
+    "version": "cpp-6.1.0",
     "url": "https://github.com/msgpack/msgpack-c/archive/__VERSION__.tar.gz",
     "use_cmake" : true,
     "defines": [