Use require() to read json custom options file

[gucong3000]

No description provided.

[stanleyhlng]

@gucong3000

Thank you for your PR. Would you mind providing some description and example about your changes?
Also, the travis build is faliing.

Error: JSON.parse error!
    at Context.<anonymous> (/home/travis/build/stanleyhlng/mocha-multi-reporters/tests/lib/MultiReporters.test.js:231:23)
    at callFn (/home/travis/build/stanleyhlng/mocha-multi-reporters/node_modules/jenkins-mocha/node_modules/mocha/lib/runnable.js:326:21)
    at Hook.Runnable.run (/home/travis/build/stanleyhlng/mocha-multi-reporters/node_modules/jenkins-mocha/node_modules/mocha/lib/runnable.js:319:7)
    at next (/home/travis/build/stanleyhlng/mocha-multi-reporters/node_modules/jenkins-mocha/node_modules/mocha/lib/runner.js:298:10)
    at Immediate._onImmediate (/home/travis/build/stanleyhlng/mocha-multi-reporters/node_modules/jenkins-mocha/node_modules/mocha/lib/runner.js:320:5)
    at tryOnImmediate (timers.js:543:15)
    at processImmediate [as _immediateCallback] (timers.js:523:5)
        ✓ throw an exception in default options
        1) throw an exception in custom options
    #test

[stanleyhlng]

build is failing for more than 2 months, please fix it and reopen the PR if necessary. Thanks!