chore: Add lint rules

[grant]

Adds google/ts-style lint rules. See @JustinBeckwith's #503 (comment). Ref: #503

Successful lint

$ npm run lint

> [email protected] lint /github/google/google-api-nodejs-client
> tslint -p . -c tslint.json
$ ...

Example erred lint

$ npm run lint

> [email protected] lint /github/google/google-api-nodejs-client
> tslint -p . -c tslint.json


ERROR: /Users/username/github/google/google-api-nodejs-client/src/index.ts[19, 29]: Unnecessary semicolon
ERROR: /Users/username/github/google/google-api-nodejs-client/src/index.ts[19, 30]: Unnecessary semicolon

npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! [email protected] lint: `tslint -p . -c tslint.json`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the [email protected] lint script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/username/.npm/_logs/2018-02-14T01_00_53_407Z-debug.log

Checks

• npm test succeeds
• Pull request has been squashed into 1 commit
• I did NOT manually make changes to anything in apis/
• Code coverage does not decrease (if any source code was changed)
• Appropriate JSDoc comments were updated in source code (if applicable)
• Appropriate changes to readme/docs are included in PR

[JustinBeckwith]

Greetings, and thanks for the PR! We already run lint as part of the gts check command that's already added. The linting is provided via tslint in this package:
https://www.npmjs.com/package/gts

[grant]

Perhaps it could be checkboxed in the issue or added to PULL_REQUEST_TEMPLATE.md.