Add priority to futures example (#214)

Author: mrocklin

Diff for: futures.ipynb

@@ -321,8 +321,8 @@
     "while seq.count() > 1:  # at least two futures left\n",
     "    a = next(seq)\n",
     "    b = next(seq)\n",
-    "    new = client.submit(add, a, b)  # add them together\n",
-    "    seq.add(new)                    # add new future back into loop"
+    "    new = client.submit(add, a, b, priority=1)  # add them together\n",
+    "    seq.add(new)                                # add new future back into loop"
    ]
   }
  ],