doc: fix typo in introduction notebook

notebooks/introduction.ipynb

@@ -217,7 +217,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Another possibility is to make an another aggregation along the tree branches, this time to compute the frequencies of the different statuses at each node. This can ben done with the `aggregate_cat` function."
+    "Another possibility is to make another aggregation along the tree branches, this time to compute the frequencies of the different statuses at each node. This can ben done with the `aggregate_cat` function."
    ]
   },
   {