Update gulp; drop gulp-webserver for gulp-connect

[drosile]

gulp-webserver has an open vulnerability. Although we only use it in dev, this replaces it with gulp-connect, which doesn't have known vulnerabilities. This also upgrades gulp, which required some non-trivial changes to the gulpfile.

[dangoor]

I looked through the code change and took a quick look at it running. It had no trouble generating the blog and I could view it in my browser right away.

Thanks for making these changes!