[Improvement] Add support for gpt4all through langchain (#838)

embedchain/embedder/gpt4all.py

@@ -1,7 +1,5 @@
 from typing import Optional
 
-from chromadb.utils import embedding_functions
-
 from embedchain.config import BaseEmbedderConfig
 from embedchain.embedder.base import BaseEmbedder
 from embedchain.models import VectorDimensions
@@ -9,12 +7,13 @@ from embedchain.models import VectorDimensions
 
 class GPT4AllEmbedder(BaseEmbedder):
     def __init__(self, config: Optional[BaseEmbedderConfig] = None):
-        # Note: We could use langchains GPT4ALL embedding, but it's not available in all versions.
         super().__init__(config=config)
-        if self.config.model is None:
-            self.config.model = "all-MiniLM-L6-v2"
 
-        embedding_fn = embedding_functions.SentenceTransformerEmbeddingFunction(model_name=self.config.model)
+        from langchain.embeddings import \
+            GPT4AllEmbeddings as LangchainGPT4AllEmbeddings
+
+        embeddings = LangchainGPT4AllEmbeddings()
+        embedding_fn = BaseEmbedder._langchain_default_concept(embeddings)
         self.set_embedding_fn(embedding_fn=embedding_fn)
 
         vector_dimension = VectorDimensions.GPT4ALL.value