Add missing import in IPython parallel magics example

examples/parallel/Parallel Magics.ipynb

@@ -36,8 +36,7 b''
      ],
      "language": "python",
      "metadata": {},
-     "outputs": [],
-     "prompt_number": 2
+     "outputs": []
     },
     {
      "cell_type": "markdown",
@@ -461,13 +460,13 b''
      "collapsed": false,
      "input": [
       "%%px --local\n",
+      "import os\n",
       "thispid = os.getpid()\n",
       "print thispid"
      ],
      "language": "python",
      "metadata": {},
-     "outputs": [],
-     "prompt_number": 5
+     "outputs": []
     }
    ],
    "metadata": {}