feat(http): add an option nameservers to query dns

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

http/client.lua

@@ -361,7 +361,8 @@ function methods:request(method, url, body, opts)
     local answers, err = dns.query(host, {
         type = opts.ipv6 and dns.TYPE_AAAA or dns.TYPE_A,
         mark = opts.mark,
-        device = opts.device
+        device = opts.device,
+        nameservers = opts.nameservers
     })
     if not answers then
         return nil, 'resolve "' .. host .. '" fail: ' .. err
@@ -432,6 +433,7 @@ end
         body_to_file: A string indicates that the body is to be written to the file.
         mark: a number used to set SO_MARK to socket
         device: a string used to set SO_BINDTODEVICE to socket
+        nameservers: see dns.query
 
     In case of failure, the function returns nil followed by an error message.
     If successful, returns a table contains the