Support `unique symbol` type (TS 2.7)

[ikatyang]

What version of TypeScript are you using?
typescript@2.7.0-dev.20171226

What version of typescript-eslint-parser are you using?
eslint/typescript-eslint-parser#e94ede3

What code were you trying to parse?

type A = unique symbol;
type B = keyof something;

What did you expect to happen?

[
  { "type": "TSTypeOperator", "operator": "TSUniqueKeyword" },
  { "type": "TSTypeOperator", "operator": "TSKeyOfKeyword"  },
]

What happened?

[
  { "type": "TSTypeOperator", "operator": 140 },
  { "type": "TSTypeOperator", "operator": 127 },
]

Ref: microsoft/TypeScript#15473

[JamesHenry]

Thanks for reporting, and thanks again @azz for already kicking off the PR.

Looks like it's time to start a branch for 2.7! As usual it won't go into master until 2.7 is the stable release.

[donaldpipowitch]

2.7 is now the stable release 💕

[JamesHenry]

Merged 👍