Fix flaky js test by not using QUnit autostart.

Previously, gulp-qunit would occasionally fail since QUnit had already started
but jquery async loading of test files had note yet completed, resulting in
errors like:

  Testing test.html
  Took 34ms to run 0 tests. 0 passed, 0 failed.
  No tests were executed. Are you loading tests asynchronously?

As part of the fix I upgraded to QUnit 2.0 since its assert.async() statement
makes this easier to handle than the QUnit.start/stop methods in QUnit 1.

Author: buge

js/test/gulpfile.js

@@ -1,7 +1,8 @@
-var gulp = require('gulp'),
-    qunit = require('gulp-qunit');
+var gulp = require('gulp');
+var qunit = require('gulp-qunit');
 
-gulp.task('default', function() {
-    return gulp.src('./test.html')
-        .pipe(qunit());
+gulp.task('test', function() {
+  return gulp.src('./test.html').pipe(qunit());
 });
+
+gulp.task('default', ['test']);