API doc problems of dropout

[ranqiu92]

针对以下问题修改时请协调组织其他内容语言

单词拼写、遗漏和语法等问题未列出，修改时请注意

请参考API注释标准！

源文件：https://github.com/PaddlePaddle/Paddle/blob/develop/python/paddle/fluid/layers/nn.py

• dropout
  http://www.paddlepaddle.org/docs/develop/api/en/fluid/layers.html#dropout
  • 缺少参考文献
  • 默认值问题（缺少或位置错误）
  • 注意事项须单独列出
  • 数据类型（variable -> Variable）

[shanyi15]

您好，此issue在近一个月内暂无更新，我们将于今天内关闭。若在关闭后您仍需跟进提问，可重新开启此问题，我们将在24小时内回复您。因关闭带来的不便我们深表歉意，请您谅解~感谢您对PaddlePaddle的支持!
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