Any time you need to run sudo something ...
to fix something, you should be pausing to think about what's going on. While the accepted answer here is perfectly valid, it's treating the symptom rather than the problem. Sorta the equivalent of buying bigger saddlebags to solve the problem of: error, cannot load more garbage onto pony. Pony has so much garbage already loaded, that pony is fainting with exhaustion.
An alternative (perhaps comparable to taking excess garbage off of pony and placing in the dump), is to run:
npm dedupe
Then go congratulate yourself for making pony happy.