fix upper version for core to 0.3 instead of 3 (#646)

pyproject.toml

@@ -15,7 +15,7 @@ httpx = ">=0.23.0" # May be able to decrease this version
 fastapi = {version = ">=0.90.1,<1", optional = true}
 sse-starlette = {version = "^1.3.0", optional = true}
 pydantic = ">=1"
-langchain-core = ">=0.1,<3"
+langchain-core = ">=0.1,<0.3"
 orjson = ">=2"
 pyproject-toml = "^0.0.10"