Fixes the import typo in the vector db text generator notebook (#1874)

Fixes the import typo in the vector db text generator notebook for the
chroma library

Co-authored-by: Anupam <anupam@10-16-252-145.dynapool.wireless.nyu.edu>

docs/modules/indexes/chain_examples/vector_db_text_generation.ipynb

@@ -28,7 +28,7 @@
     "from langchain.docstore.document import Document\n",
     "import requests\n",
     "from langchain.embeddings.openai import OpenAIEmbeddings\n",
-    "from langchain.vectorstores import Chromama\n",
+    "from langchain.vectorstores import Chroma\n",
     "from langchain.text_splitter import CharacterTextSplitter\n",
     "from langchain.prompts import PromptTemplate\n",
     "import pathlib\n",