Update internal.lua (#1237)

修正小错误。

lualib/http/internal.lua

@@ -1,5 +1,6 @@
 local table = table
 local type = type
+local sockethelper = require "http.sockethelper"
 
 local M = {}
 
@@ -170,7 +171,7 @@ function M.request(interface, method, host, url, recvheader, header, content)
 	local tmpline = {}
 	local body = M.recvheader(read, tmpline, "")
 	if not body then
-		error(socket.socket_error)
+		error(sockethelper.socket_error)
 	end
 
 	local statusline = tmpline[1]