Fix formatting in sequential chat notebook (#1914)

Author: jackgerrits

notebook/agentchats_sequential_chats.ipynb

@@ -78,6 +78,7 @@
     "### Solve tasks with a series of chats\n",
     "\n",
     "The `autogen.initiate_chats` interface can take a list of dictionaries as inputs. Each dictionary preserves the following fields: \n",
+    "\n",
     "- `sender`: a conversable agent as the sender;\n",
     "- `recipient`: a conversable agent as the recipient;\n",
     "- `message`: is a string of text (typically a message containing the task);\n",