set ndots to 1 when none parsed from resolv.conf

as per https://www.man7.org/linux/man-pages/man5/resolv.conf.5.html, default is 1

lib/httpx/resolver/native.rb

@@ -30,7 +30,7 @@ module HTTPX
         nameserver = nameserver[family] if nameserver.is_a?(Hash)
         Array(nameserver)
       end
-      @ndots = @resolver_options[:ndots]
+      @ndots = @resolver_options.fetch(:ndots, 1)
       @search = Array(@resolver_options[:search]).map { |srch| srch.scan(/[^.]+/) }
       @_timeouts = Array(@resolver_options[:timeouts])
       @timeouts = Hash.new { |timeouts, host| timeouts[host] = @_timeouts.dup }