build:change gulp clean dist dir (#2582)

Author: limerickgds

tools/gulp/tasks/clean.ts

@@ -1,5 +1,6 @@
 import {task} from 'gulp';
+import {DIST_ROOT} from '../constants';
 import {cleanTask} from '../task_helpers';
 
 
-task('clean', cleanTask('dist'));
+task('clean', cleanTask(DIST_ROOT));