fix(spin_sdk): fix up http:send

Signed-off-by: Vaughn Dice <vdice@akamai.com>

Author: vdice

examples/outgoing-request/app.py

@@ -12,4 +12,4 @@ async def handle_request(self, request: Request) -> Response:
                 bytes("Please specify `url` header", "utf-8")
             )
 
-        return send(Request("GET", url, {}, None))
+        return await send(Request("GET", url, {}, None))

src/spin_sdk/http/__init__.py

@@ -200,7 +200,7 @@ async def send(request: Request) -> Response:
         status,
         dict(map(
             lambda pair: (pair[0], str(pair[1], "utf-8")),
-            headers.entries()
+            headers
         )),
         bytes(body)
     )