emit progress event for put Buffer

[datenstau]

Hi, I had the use case of putting a >30 MB Buffer to a server and there was no progress event emitted. So I added a quick fix for this. Maybe you would like to add this to jsftp.

[sergi]

Hi @datenstau, thanks for your PR. Unfortunately is not passing tests (there are none) and it's not following the code style guidelines (jsftp is not writen in ES6 because, among other things, we want to be compatible with Node 0.12). Can you fix those?

[skg54]

Thanks for your contribution @datenstau