feature: root option allows array of strings

src/util/promise.js

@@ -0,0 +1,19 @@
+const Promise = require('any-promise');
+
+/*
+ * Call functions in serial until someone resolved.
+ * @param {Array} iterable the array to iterate with.
+ * @param {Array} iteratee returns a new promise.
+ * The iteratee is invoked with three arguments: (value, index, iterable). 
+ */
+function someSeries(iterable, iteratee) {
+    var ret = Promise.reject(new Error('init'));
+    iterable.forEach(function(item, idx) {
+        ret = ret
+            .then(x => x)
+            .catch(e => iteratee(item, idx, iterable));
+    });
+    return ret;
+}
+
+exports.someSeries = someSeries;