Allow async/await on mocha it handler.

mocha-async.js

/**
 * If you do:
 * describe('Test', ()=>{
 *   it('what', async (done)=>{
 *     try{
 *       await SOME_ASYNC_FUNCTION
 *       done()
 *     }catch(e){
 *       done(e)
 *     }
 *   });
 * });
 *
 * You'll most likely get an error:
 *   Error: Resolution method is overspecified. Specify a callback *or* return a Promise; not both.
 *
 * To solve that, just add these lines before any of your tests.
 * It just overwrites the mocha "it" function so not complain about the overspecification.
 */
const _it = it;
global.it = function(txt, cb){
  _it(txt, (done)=>{
    cb(done);
  });
}