ci: add semantic-release

[austince]

Integrates semantic-release so we don't have to make chore commits or bog Keith down with releasing 🎈

Flow:

• only releases on master
• analyzes the commits to determine the type of release (Major, Minor, Patch, no release)
• creates a git tag
• creates an npm release
• creates a github release
• generates a changelog from commits

If you'd like to test it locally, run npm run release -- --branch build/semantic-release --dry-run

Also:

• removes the README build script, as it seems that hasn't been used in a long time (please let me know if this isn't the case)
• only runs coverage reporting after the tests succeed in ci (coveralls can fail in local envs - we could also move to codecov)
• adds more current node versions to ci testing

P.S. the massive diff is mostly the package lock - no fear!

Closes #91 Closes #92

[austince]

@keithamus :sweat_smile: that's the only unfortunate part - I merged this locally, did a dry-run, and no release was made as expected. Should we wait for someone else to take a look at this as well?

[keithamus]

Sounds like a good plan. @meeber @lucasfcosta?

[austince]

I'll be available tomorrow if we want to merge it then!

[austince]

@keithamus @lucasfcosta @vieiralucas looks like the GitHub token that's in the CI doesn't have proper permissions to push tags. Who's token should we update it with? The secure NPM token from .travis.yml might also be getting overwritten by the Travis repository settings.