Replace example repository

[joelpurra]

• The example Level/leveldown no longer depends on prebuild-install.
• A popular dependent is lovell/sharp, with 35k+ downloads for release v0.25.2.

See

• https://www.npmjs.com/package/prebuild-install?activeTab=dependents
• https://github.com/lovell/sharp/releases/tag/v0.25.2
• https://github.com/prebuild/prebuild-stats/issues/1

Fixes #1.

[vweevers]

Thanks!