chore: Enable yarn package management

[joshwiens]

Description

Enables the use of the Yarn package manager in a limited fashion.

What's included?

• Adds a yarn.lock file, treated as a binary using .gitattributes ( prevents merge conflict hell )
• Modifies .travis.yml to install using yarn
  • Adds a rebuild step for node-sass. Issue documented in build file & readme.
  • yarn install saves 40 - 50 seconds on the install, ~6 of which are lost on the rebuild.
• Modifies .travis.yml to build only develop & master plus any open pull request
  • Currently all your builds are running twice. Call it a courtesy to Travis :)
• Picks up latest PhantomJS for Installing phantomjs-prebuilt fails due to no npm_config_tmp yarnpkg/yarn#1538
  • *nix related tmp directory / permissions problem in phantom / yarn.

General Tests for Every PR

• ng serve --aot still works.
• npm run lint passes.
• npm test passes and code coverage is not lower.
• npm run build still works.

A note about using yarn.

Speed & deterministic install benefits aside, using Yarn comes with a bit of baggage. The lock file is something that has to be maintained to be of any real value.

Any PR that changes a package version will also have to update the lock file accordingly. Simplest way to do that is to make the changes via yarn, optionally you can use npm and rm -rf yarn.lock && yarn install to pick up the dependency changes in the pull request.

The lock file is then committed along with any other versioned file. Certainly not a major issue but it is something that has to become part of the development process at the maintainer level.

Closes #313

[emoralesb05]

Awesome @d3viant0ne ! No more double builds 💥

[joshwiens]

Sorry about the delay, completely forgot about #313 until I looked at the beta.3 milestone :)

[emoralesb05]

w00t, thanks again!