Upgrade to v6.5.0

[ncoden]

Upgrade foundation-sites to v6.5.0

Changes

• Update Foundation assets
• Update Rakefile to use the new assets
• Update Gem lockfiles
• Drop Ruby 2.2. Tests are now run on Ruby 2.3, 2.4 and 2.5

See https://github.com/zurb/foundation-sites/releases/tag/v6.5.0