file download is always append, and does not offer the ability to overwrite

[lorgio]

The WriteSteam is set to append, which sometimes is an issue, if you're creating a script that needs to always download a file. It should have the ability to overwrite the file, rather than append to it.

https://github.com/wuchengwei/node-wget/blob/master/lib/wget.js#L36

[anthony-stephan]

+1

[azachar]

+1

[AntoineTurmel]

@wuchengwei possible to merge this :) ? (or add an option to switch between append/write) ?