fix import errors (#710)

Author: jonhealy1

docs/src/tips-and-tricks.md

@@ -55,8 +55,8 @@ The [**Fields** API extension](https://github.com/stac-api-extensions/fields) en
 from typing import Optional, Set
 
 import attr
-from stac_fastapi.extensions import FieldsExtension as FieldsExtensionBase
-from stac_fastapi.extensions.core.fields import requests
+from stac_fastapi.extensions.core import FieldsExtension as FieldsExtensionBase
+from stac_fastapi.extensions.core.fields import request
 from pydantic import BaseModel, Field