Modernize wfs-client

[tusbar]

• Use yarn instead of npm [sorry]
• Use xo instead of custom eslint config
• Use async/await
• Upgrade libxmljs
• Require node > 8
• Remove superagent and use got
  • Let got concat each buffer chunk instead of doing it manually
  • Get rid of the double callback! warnings

This change fixes some issues where errors would be swallowed. For example, http://geobretagne-migration.fr/geoserver/rff/wfs used to throw a Version negociation failed error while the error was in fact that the DNS doesn’t resolve.

[jdesboeufs]

🤪