此方法现在返回对 writable 的引用。
writable
新增于: v0.11.15
encoding
writable.setDefaultEncoding() 方法为 Writable 流设置默认的 encoding。
writable.setDefaultEncoding()
Writable
This method now returns a reference to writable.
Added in: v0.11.15
The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.