Include "npm update " in upgrade

[excellme]

Today I upgraded my forum from v0.4.1 to v0.4.3 . When upgrading ,I got some trouble such as widget error.I solved these problems by upgrading my dependency npm upgrade ,eventually.
I think maybe It's better to include npm update in nodebb upgrade command

[julian]

We'd probably have to roll our own upgrade script that calls npm install with a version number. npm upgrade is too risky, since it downloads the latest version of a module, irrespective of any configured versioning in your package.json.

Our themes and plugins aren't comparible with older versions, so they might end up installing a version that is too new and break their forum...