updates example command to be consistent with text

examples/Embedding_Wikipedia_articles_for_search.ipynb

@@ -51,7 +51,7 @@
     "Install any missing libraries with `pip install` in your terminal. E.g.,\n",
     "\n",
     "```zsh\n",
-    "pip install tiktoken\n",
+    "pip install openai\n",
     "```\n",
     "\n",
     "(You can also do this in a notebook cell with `!pip install openai`.)\n",