specs: upgrade to bootstrap v5.0.2 (#235)

Author: mr-c

site/cwlsite.cwl

@@ -103,7 +103,7 @@ steps:
       extra: {source: render, valueFrom: $(self.extra)}
       brandstyle:
         default: |
-          <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css" integrity="sha384-604wwakM23pEysLJAhja8Lm42IIwYrJ0dEAqzFsj9pJ/P5buiujjywArgPCi8eoz" crossorigin="anonymous" />
+          <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" integrity="sha384-EVSTQN3/azprG1Anm3QDgpJLIm9Nao0Yz1ztcQTwFspd3yD65VohhpuuCOmLASjC" crossorigin="anonymous" />
           <link rel="stylesheet" href="/assets/styles-fix.css" />
           <link rel="shortcut icon"
           href="https://www.commonwl.org/user_guide/_static/images/favicons/cwl/favicon-96x96.png" />