Fix type of aiohttp raw headers (#161)

Author: rsmeral

src/pook/interceptors/aiohttp.py

@@ -139,7 +139,9 @@ async def _on_request(
         _res.reason = http_reasons.get(res._status)
 
         # Add response headers
-        _res._raw_headers = tuple(headers)
+        _res._raw_headers = tuple(
+            [(bytes(k, "utf-8"), bytes(v, "utf-8")) for k, v in headers]
+        )
         _res._headers = multidict.CIMultiDictProxy(multidict.CIMultiDict(headers))
 
         if res._body: