Flatten futures

Sources/GzipMiddleware/GzipMiddleware.swift

@@ -51,14 +51,15 @@ public struct GzipServerMiddleware: Middleware, ServiceType {
                             return stream.write(.chunk(buffer))
                         }
                     })
-                write.always {
+                _ = write.flatMap {
                     buffer.clear()
                     buffer.write(integer: crc32, endianness: .little)
                     buffer.write(integer: UInt32(data.count), endianness: .little)
-                    stream.write(.chunk(buffer)).always {
+                    return stream.write(.chunk(buffer))
-                        _ = stream.write(.end)
+                }.flatMap {
-                    }
+                    return stream.write(.end)
-                }
+                }.transform(to: ())
+
                 let httpResponse = HTTPResponse(status: response.http.status, headers: headers, body: stream)
                 return request.response(http: httpResponse)
             }