Minor fix in recipe 8.2.

Author: rossant

notebooks/chapter08_ml/02_titanic.ipynb

@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:0d6b1522cdbb0c5a52efd1123fe34763d5fcd2abb8f3450b7c4f4d3baf164af4"
+  "signature": "sha256:2acac914c799bf86aab2e831a8397628cdf323d08ac02a97db61a4ad017625c0"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -101,7 +101,7 @@
      "cell_type": "code",
      "collapsed": false,
      "input": [
-      "data = train[['Sex', 'Age', 'Pclass', 'Survived']]\n",
+      "data = train[['Sex', 'Age', 'Pclass', 'Survived']].copy()\n",
       "data['Sex'] = data['Sex'] == 'female'\n",
       "data = data.dropna()"
      ],