Tighten a type. Bump TS generator version. Format Travis type error.

[aomarks]

• Make EventApi.path's EventTarget type non-nullable.
• Bump TypeScript generator version.
• Make Travis update-types failure style the same as the elements.

[aomarks]

Hmm, Travis is failing because package-lock.json changed. I guess npm install can do that? Not sure why this never came up before though. I'm doing it through npm run update-types instead of gulp update-types now, but it should be the exact same thing.

[googlebot]

So there's good news and bad news.

👍 The good news is that everyone that needs to sign a CLA (the pull request submitter and all commit authors) have done so. Everything is all good there.

😕 The bad news is that it appears that one or more commits were authored by someone other than the pull request submitter. We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that here in the pull request.

Note to project maintainer: This is a terminal state, meaning the cla/google commit status will not change from this State. It's up to you to confirm consent of the commit author(s) and merge this pull request when appropriate.

[TimvdLippe]

@aomarks I have regenerated the lock file with npm 5.6.0. Not sure why your original install did not fully "lock" the lockfile.

[TimvdLippe]

Nice. Congrats on the stable release!