Please add "Retry" option if download fails

[cyp0633]

Is your feature request related to a problem? Please describe.
In China Mainland, the connection quality to international sites (such as GitHub) is usually poor, so my download process is often interrupted because of timeout, etc. That means I have to restart the whole deploying process from the beginning.

Describe the solution you'd like
I wonder if you could add a "retry" option to retry downloading a certain file which failed to get downloaded. That could save a lot of time of meaningless downloading.

Describe alternatives you've considered
I tried to use network from another ISP, but it was still really slow (about 30KB/s), and there was still a risk of failure.
When I used ShadowsocksR (a kind of proxy), it got even slower and more timeout occurred. That was a problem of my proxy server and I've got it solved.
Downloading the files by myself is much faster. I could find the project files on GitHub, but I didn't know where to put them to make the deployer identify them.