TypeScript 2.8 & 2.9 adaptations (dependencies & tests)

[kobim]

PR checklist

• Addresses an existing issue: #0000
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of changes:

As a dependant module with npm 2.x

Adding typescript 2.9.0-dev to peerDependencies, as modules depending on "typescript": "next" and tslint are failing to install with npm version 2.x (as npm versions prior to 3 were failing unmet peerDependencies):

npm ERR! peerinvalid The package typescript@2.9.0-dev.20180324 does not satisfy its siblings' peerDependencies requirements!
npm ERR! peerinvalid Peer tslint@5.9.1 wants typescript@>=2.1.0 || >=2.1.0-dev || >=2.2.0-dev || >=2.3.0-dev || >=2.4.0-dev || >=2.5.0-dev || >=2.6.0-dev || >=2.7.0-dev || >=2.8.0-dev

package.json:

"devDependencies": {
  "tslint": "^5.9.1",
  "typescript": "next"
}

Updates for TypeScript 2.8+

Many places previously returned empty string as text when JSDoc declaration had no comment, but now it returns undefined and it was failing the tests for typescript@next.

Is there anything you'd like reviewers to focus on?

-- none --

CHANGELOG.md entry:

[bugfix] Using tslint with typescript 2.9.0 would cause errors under npm 2.x

[palantirtech]

Thanks for your interest in palantir/tslint, @kobim! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[jkillian]

Thanks so much for making these fixes @kobim! This got lost in the shuffle unfortunately, and it looks like #3819 and #3853 cover the changes this PR had, so going to close this out