message: use a tmpdir that's writable on travis
diff: /* eslint-env node */
  'use strict';
  +const os = require('os');
  +
  module.exports = function(/* deployTarget */) {
  let ENV = {
  build: {
  environment: 'production'
  + },
  + git: {
  + worktreePath: `${os.tmpdir()}/deploy-box`
  }
  };
  return ENV;
  