Save uploaded files in optional --save-dir

lib/units/storage/temp.js

@@ -84,6 +84,9 @@ module.exports = function(options) {
 
   app.post('/s/upload/:plugin', function(req, res) {
     var form = new formidable.IncomingForm()
+    if (options.saveDir) {
+      form.uploadDir = options.saveDir
+    }
     Promise.promisify(form.parse, form)(req)
       .spread(function(fields, files) {
         return Object.keys(files).map(function(field) {