add missing sys import

docs/examples/parallel/Parallel Magics.ipynb

@@ -89,6 +89,16 b''
      "cell_type": "code",
      "collapsed": false,
      "input": [
+      "with dv.sync_imports():",
+      "    import sys"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
       "%px print >> sys.stderr, \"ERROR\""
      ],
      "language": "python",