fix run scenario from remixd

src/app/tabs/run-tab.js

@@ -327,7 +327,10 @@ function makeRecorder (events, appAPI, appEvents) {
   }
   runButton.onclick = () => {
     var currentFile = appAPI.config.get('currentFile')
-    var json = appAPI.filesProviders['browser'].get(currentFile)
+    appAPI.fileProviderOf(currentFile).get(currentFile, (error, json) => {
+      if (error) {
+        modalDialogCustom.alert('Invalid Scenario File ' + error)
+      } else {
         if (currentFile.match('.json$')) {
           try {
             var obj = JSON.parse(json)
@@ -349,6 +352,8 @@ function makeRecorder (events, appAPI, appEvents) {
           modalDialogCustom.alert('A Scenario File is required. The file must be of type JSON. Use the "Save Transactions" Button to generate a  new Scenario File.')
         }
       }
+    })
+  }
   return { recordButton, runButton }
 }
 /* ------------------------------------------------