Tweak `files` type hints (#976)

diff --git a/httpx/_types.py b/httpx/_types.py
index f124bf702421bfc72fc506c468bb8f5b44e1cffd..f5f17c5e10f29665629a122037553dd6917ad92a 100644 (file)
--- a/httpx/_types.py
+++ b/httpx/_types.py
@@ -65,4 +65,4 @@ FileTypes = Union[
     # (filename, file (or text), content_type)
     Tuple[Optional[str], FileContent, Optional[str]],
 ]
-RequestFiles = Dict[str, FileTypes]
+RequestFiles = Mapping[str, FileTypes]