cross-ci/lib/var/IS_CI.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.

const envCi = require('../envCi');

/// Boolean indicating if script runs in a CI environment.
const IS_CI = ({CI_PLATFORM}) =>
    Boolean(
        (CI_PLATFORM && (CI_PLATFORM !== '___UNKNOWN_CI_PLATFORM___'))
        || process.env.CI
        || envCi.isCi
    );

module.exports = IS_CI;