issue #95 - restore parse5 typings for ASTAttribute

[atsu85]

Make sure you check the following:

• [ ] you are making a pull request for the develop branch
• [ ] unless trivial, a corresponding issue exists for this PR (reference it)
• [ ] if this PR fixes the issue, then include fix #
• [ ] you've ran gulp test and it passes the lint
• [ ] tests don't fail (except tests in 'failing.spec.ts')

**Note:* Requests to pull into master from a fork will be rejected.*

[MeirionHughes]

I'll merge this, but I suspect I'll rework all of those classes in the new few weeks. (I'm away next week btw).