GLOBAL is going away, use global instead

[ChALkeR]

See nodejs/node#1838.

Your code, as of version 1.14.0:

54087   ioredis-1.14.0.tgz/test/helpers/global.js:9:GLOBAL.MockServer = require('./mock_server');
54087   ioredis-1.14.0.tgz/test/helpers/global.js:8:GLOBAL.Redis = require('../..');
54087   ioredis-1.14.0.tgz/test/helpers/global.js:6:GLOBAL.stub = sinon.stub.bind(sinon);
54087   ioredis-1.14.0.tgz/test/helpers/global.js:3:GLOBAL.expect = require('chai').expect;

There could be other places, better double-check this.