Fix a typo in the summarization use case. (#12316)

- **Description:** Fix a tiny typo in the summarization use case Jupyter
notebook.
  - **Issue:** N/A
  - **Dependencies:** N/A
  - **Tag maintainer:** @hwchase17
  - **Twitter handle:** @seasonsaw

docs/docs/use_cases/summarization.ipynb

@@ -290,7 +290,7 @@
     "\n",
     "Let's unpack the map reduce approach. For this, we'll first map each document to an individual summary using an `LLMChain`. Then we'll use a `ReduceDocumentsChain` to combine those summaries into a single global summary.\n",
     " \n",
-    "First, we specfy the LLMChain to use for mapping each document to an individual summary:"
+    "First, we specify the LLMChain to use for mapping each document to an individual summary:"
    ]
   },
   {