Fix a few bugs

[btoews]

This PR fixes two bugs:

• Whitespace wasn't allowed around the return type from a promise.
• Dictionary members couldn't be prefixed with the required keyword.

These fixes allow this gem to parse the IDL from the Web Authentication spec.

[coveralls]

Coverage increased (+0.1%) to 94.892% when pulling 7ebd05e on mastahyeti:master into 18cf050 on jarib:master.

[jarib]

Thanks! It's been a while since the specs ran on Travis. If you rebase this against master the build should be fixed.

[coveralls]

Coverage increased (+0.1%) to 94.892% when pulling 43c545d on mastahyeti:master into 81ca9e1 on jarib:master.

[jarib]

Merged and released as 0.1.9.

[btoews]

🙇