Allow value-less dash-cased props

Currently you can't pass down dash-cased properties without a value.

See error case here in REPL.

// current
{ 'data-foo' }

// w/ update
{ 'data-foo': true }

Changes

• Add true to output if contains dashed and non-value
• Refactor if/else into named functions
• data-attribute -> any dash-cased prop
• Add test

Pipeline issue should be fixed with https://gitlab.com/Rich-Harris/buble/merge_requests/120

Merged into https://github.com/Rich-Harris/buble (am moving this repo over to GitHub), will release soon. Thanks!

closed