cross-ci/lib/var/PROJECT_VERSION.js

`cross-ci` standardizes environment variables for CI. For example, your can simply use `BUILD_BRANCH` variable in all CI runners instead of `CIRCLE_BRANCH` in CircleCI or `TRAVIS_PULL_REQUEST_BRANCH` in Travis.

/// Semver version of your project. Taken from `package.json`. Othewise
/// defaults to `0.0.0`.
const pkg = require('../pkg');

const PROJECT_VERSION = () =>
    typeof pkg.version === 'string'
        ? pkg.version
        : '0.0.0';

module.exports = PROJECT_VERSION;