Fix: Attempt to cache dependencies installed with composer

[localheinz]

This PR

• attempts to cache dependencies installed with composer between builds (faster builds)
• authenticates with the GitHub API (requires work by you, @bighappyface)

Follows #222 (comment).

💁 This should cut down the build time significantly; after all, more than 95% of the build time are spent on cloning the dependencies.

[localheinz]

@bighappyface

You actually need to create a GitHub token and ideally encrypt it, then replace the result here (use the actual token, not foo, of course).

For this you need to install https://github.com/travis-ci/travis.rb if you haven't already.

Then run

$ travis encrypt GITHUB_TOKEN=foo

from within your local clone of justinrainbow/json-schema, generating output similar to this:

Please add the following to your .travis.yml file:

  secure: "..."

Pro Tip: You can add it automatically by running with --add.

💁 Do not use --add, it just messes up .travis.yml by rewriting it.

[localheinz]

@bighappyface

Alternatively, you can - of course - specify a GITHUB_TOKEN in Travis!

[bighappyface]

@localheinz I am on the fence about this one.

First, I am a collaborator but not the owner of the repo, so I can't configure repo settings. Push/pull only.

Second, I am wondering if we could achieve essentially the same (or better) performance improvement by bringing composer.lock back into the repo. I know on many other projects that I work with having composer.lock makes the biggest difference that I can feel.

[localheinz]

@bighappyface

Both make a lot of sense!

[bighappyface]

Closing for now