Assign a dummy value to the `docBaseUrl` API parameter in non-`PRODUCTION` mode

This ensures that relative links are displayed when using the viewer in `gulp server` mode, in an effort to aid development/debugging.

web/app.js

@@ -658,7 +658,9 @@ let PDFViewerApplication = {
       this.setTitleUsingUrl(file.originalUrl);
       parameters.url = file.url;
     }
-    if (typeof PDFJSDev !== 'undefined' &&
+    if (typeof PDFJSDev === 'undefined' || !PDFJSDev.test('PRODUCTION')) {
+      parameters.docBaseUrl = document.URL.split('#')[0];
+    } else if (typeof PDFJSDev !== 'undefined' &&
                PDFJSDev.test('FIREFOX || MOZCENTRAL || CHROME')) {
       parameters.docBaseUrl = this.baseUrl;
     }