adds check for file existance before returning;
adds a class to do repository validation on what’s stored locally;
updates the local cache middleware to validate that the cache is correct if a request for component.json is received, the assumption is that a request for component.json means there will be follow-up requests for the individual files.  If validation fails the entire cached repo directory is removed and it’s forwarded to the next middleware;
fixses the bug where we could try extracting the zip before all data was written;
Updates the private github cache to do validation of the downloaded and extracted archive;
adds missing semi-colon;
removes some logging;
adds a bug where we call next then don’t return;
copies the file only once the ‘finish’ event has been raised and the stream is fully flushed;
Merge branch 'master' into support-offline-mode

Conflicts:
	lib/private-github-cache.js
Merge pull request #4 from virtru/support-offline-mode

Support offline mode