clean target fails if the files to delete is not present

--- a/gulpfile.js
+++ b/gulpfile.js
@@ -70,7 +70,7 @@
 
 gulp.task('build', done => {
     let runSequence = require('run-sequence');
-    runSequence('clean', ['build:lib', 'build:docs', 'build:package'], done);
+    runSequence(['build:lib', 'build:docs', 'build:package'], done);
 });
 
 // Tests