fix(watch): Run sync, to prevent errors from race conditions

build/tasks/watch.js

@@ -1,9 +1,18 @@
-var gulp  = require('gulp');
-var gutil = require('gulp-util');
+var gulp        = require('gulp');
+var gutil       = require('gulp-util');
+var runSequence = require('run-sequence');
 
-gulp.task('watch', ['clean', 'build-commonjs'], function() {
+gulp.task('attach-watchers', function () {
   return gulp.watch(['src/**/*', 'test/**/*'], ['build']).on('change', function(file) {
-
     gutil.log('File ' + file + ' was changed, running tasks...');
   });
 });
+
+gulp.task('watch', function(callback) {
+  return runSequence(
+    'clean',
+    'build-commonjs',
+    'attach-watchers',
+    callback
+  );
+});