changed cohere.py to update the default model of embedding (#4709)

# The cohere embedding model do not use large, small. It is deprecated.
Changed the modules default model

Fixes #4694


Co-authored-by: rajib76 <rajib76@yahoo.com>
Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

langchain/embeddings/cohere.py

@@ -18,11 +18,13 @@ class CohereEmbeddings(BaseModel, Embeddings):
         .. code-block:: python
 
             from langchain.embeddings import CohereEmbeddings
-            cohere = CohereEmbeddings(model="medium", cohere_api_key="my-api-key")
+            cohere = CohereEmbeddings(
+                model="embed-english-light-v2.0", cohere_api_key="my-api-key"
+            )
     """
 
     client: Any  #: :meta private:
-    model: str = "large"
+    model: str = "embed-english-v2.0"
     """Model name to use."""
 
     truncate: Optional[str] = None