Exclude "modified date" for Firefox/Android

## Issue
It appears that the modification date of the Android file changes when selected, so that file was deemed "different" when trying to resume upload.

## Change
Exclude modification date for now. Let's assume a smart user.

ui/util/file.js

@@ -1,8 +1,5 @@
 // @flow
 
 export function serializeFileObj(file: File) {
-  // $FlowFixMe - these are non standard, but try to include anyway.
+  return `${file.name}#${file.type}#${file.size}`;
-  const aux = `${String(file.lastModifiedDate)}#${String(file.webkitRelativePath)}`;
-
-  return `${file.name}#${file.type}#${file.size}#${file.lastModified}#${aux}`;
 }