http: rename CURLOPT_FILE to CURLOPT_WRITEDATA

The CURLOPT_FILE name is an alias for CURLOPT_WRITEDATA, the
CURLOPT_WRITEDATA name has been preferred since curl 7.9.7, released
in May 2002[1].

1. https://curl.se/libcurl/c/CURLOPT_WRITEDATA.html

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/http-walker.c b/http-walker.c
index 19e3162..910fae5 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -378,7 +378,7 @@ static void fetch_alternates(struct walker *walker, const char *base)
 	alt_req.walker = walker;
 	slot->callback_data = &alt_req;
 
-	curl_easy_setopt(slot->curl, CURLOPT_FILE, &buffer);
+	curl_easy_setopt(slot->curl, CURLOPT_WRITEDATA, &buffer);
 	curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
 	curl_easy_setopt(slot->curl, CURLOPT_URL, url.buf);