Add timestamp to export-filename

NEWS.md

@@ -35,6 +35,7 @@
 - RSS feed will be fetched more reliably ([#1052](https://github.com/SSilence/selfoss/pull/1052))
 - More of user interface is now translatable ([#1054](https://github.com/SSilence/selfoss/pull/1054))
 - Open Sans font is no longer bundled, resulting in smaller installations. Additionally, `use_system_font` option was removed. The typeface is still set as the default font family, so if you want to use it, install it to your devices. If you want to use a different typeface, add `body { font-family: 'Foo Face'; }` to your `user.css`. ([#1072](https://github.com/SSilence/selfoss/pull/1072))
+- The file name of exported sources now includes a timestamp ([#1078](https://github.com/SSilence/selfoss/pull/1078))
 
 
 ## 2.18 – 2018-03-05

controllers/Opml.php

@@ -343,7 +343,8 @@ public function export() {
         \F3::get('logger')->debug('finished OPML export');
 
         // save content as file and suggest file name
-        header('Content-Disposition: attachment; filename="selfoss-subscriptions.xml"');
+        $exportName = 'selfoss-subscriptions-' . date('YmdHis') . '.xml';
+        header('Content-Disposition: attachment; filename="' . $exportName . '"');
         header('Content-Type: text/xml; charset=UTF-8');
         echo $this->writer->outputMemory();
     }