AIOHTTP Filename upload (#241)

* add the option to specify a filename on AIOHTTPTransport multipart upload

Author: pkucmus

CONTRIBUTING.md

@@ -31,7 +31,7 @@ virtualenv gql-dev
 Activate the virtualenv and install dependencies by running:
 
 ```console
-python pip install -e.[dev]
+python -m pip install -e.[dev]
 ```
 
 If you are using Linux or MacOS, you can make use of Makefile command

gql/transport/aiohttp.py

@@ -185,7 +185,7 @@ async def execute(
 
             # Add the extracted files as remaining fields
             for k, v in file_streams.items():
-                data.add_field(k, v, filename=k)
+                data.add_field(k, v, filename=getattr(v, "name", k))
 
             post_args: Dict[str, Any] = {"data": data}