Bad advice when using npx

[tamzinblake]

In this example, npx is using the locally-installed version of bower (node_modules/.bin/bower). update-notifier is correctly noticing that we're not using the latest version, but it suggests that npm i -g bower will fix that, which it will not, since it'll still use the locally-installed version, which is old.

=> $ npm -v
5.0.3
=> $ node -v
v6.9.5
=> $ npx -v
4.0.3

[sindresorhus]

I think we should make the isGlobal option default to auto-detecting whether it's installed globally or locally. Right now you have to set it manually. Can use the is-installed-globally package. Pull request welcome.

[tamzinblake]

For reference: https://github.com/yeoman/update-notifier#isglobal