[Feature request] update delay

[mistic100]

I am using TravisCI and Greenkeeper on my project.

All recent dependencies updates failed because the new published version of the package wasn't available yet on the repository. Maybe TravisCI is using a custom NPM proxy which is not immediately updated, or it hits a NPM server which is not update yet (NPM network is known to be sometimes slow to synchronize).

Would it be possible to configure Greenkeeper to wait (let's say a day) before trying to apply a new version ?

Exemple of failed updates https://github.com/mistic100/squareicon/issues?q=is%3Aissue+is%3Aclosed none of those were actually failing but I had to manually create the PR and close the issue openned by the bot.