Fix typo in introduction.ipynb.

Fix typo 'relvant' to 'relevant'.

chapter01_crashcourse/introduction.ipynb

@@ -310,7 +310,7 @@
     "Consider, for example a set of data harvested \n",
     "from a database of home sales.\n",
     "We might construct a table, where each row corresponds to a different house, \n",
-    "and each column corresponds to some relvant attribute,\n",
+    "and each column corresponds to some relevant attribute,\n",
     "such as the square footage of a house, the number of bedrooms, the number of bathrooms,\n",
     "and the number of minutes (walking) to the center of town. \n",
     "Formally, we call one row in this dataset a *feature vector*,\n",