NPM >v5 breaks on installing the package

[ntsaini]

@jthomas someone opened up an issue on my repo and since my module has similar dependencies as yours, it suffers from the same breaking changes caused by npm > v5.0

In short if you install the package on a machine using npm v5, npm breaks and will not install any other node red package afterwards.

The fix is simply to update the dependency in package.json to "npm":"^5.6.0"