display npm package version

The https://badge.fury.io/ service is used to display the latest version of the project's npm package.

A quick look at the GitHub's project page may then tell any user if an upgrade is available (without visiting https://npmjs.org/package/sqlite3 manually for this purpose).

A hyperlink to https://npmjs.org/package/sqlite3 is still available so that the package's version can be confirmed whenever the user feels that https://badge.fury.io/ service is less trusted (or if https://badge.fury.io/ is simply down, though the latter I haven't experienced yet).