Add deploy task in gulpfile.js (#39)

[michealbenedict]

This PR addresses two things

1. 39 by adding a deploy task to gulpfile.js

2. Update versions of dependencies in package.json

The gulp task deploy (using gulp-gh-pages plugin) does the following:

1. Clone remote repo
2. Checkout gh-pages branch (create if it doesn't exist)
3. Copy files specified in gulp.src
4. Add files (if no new changes are detected, it stops here)
5. Commit with message "Updates"
6. Push to remote

The task looks as below.

gulp.src([])
.pipe(deploy(gitRemoteUrl, remote) // plugin emits the files for further piping

Again, feedback appreciated.

[addyosmani]

LGTM. Thanks a bunch @rowoot! :) cc @sindresorhus for a review before we land this.

[sindresorhus]

lgtm2 :)