fixed "remaining" column in WebUI

the key had the wrong name. In the js code, the expected key is "amount_left" and not "remaining".

src/webui/btjson.cpp

@@ -103,7 +103,7 @@ static const char KEY_TORRENT_AMOUNT_DOWNLOADED[] = "downloaded";
 static const char KEY_TORRENT_AMOUNT_UPLOADED[] = "uploaded";
 static const char KEY_TORRENT_AMOUNT_DOWNLOADED_SESSION[] = "downloaded_session";
 static const char KEY_TORRENT_AMOUNT_UPLOADED_SESSION[] = "uploaded_session";
-static const char KEY_TORRENT_AMOUNT_LEFT[] = "remaining";
+static const char KEY_TORRENT_AMOUNT_LEFT[] = "amount_left";
 static const char KEY_TORRENT_AMOUNT_COMPLETED[] = "completed";
 static const char KEY_TORRENT_RATIO_LIMIT[] = "ratio_limit";
 static const char KEY_TORRENT_LAST_SEEN_COMPLETE_TIME[] = "seen_complete";