update dependencies

[mapsam]

Updates dependencies to resolve security issues:

• update geojson-coords to 0.0.1 Update dependency geojson-flatten to resolve outdated geojson-flatten audit. geojson-coords#4
• update eslint to a more modern version
• test with node 10/12 on travis

This will go out as 0.4.0 and include #5 - cc @ajashton

[ajashton]

👍