Website: don't crash horribly on error doc problem

If a problem is detected with some error documentation, we used to show
the problem on the error page in a nice red box. This broke after some
refactoring, and now the whole page crashes with a ReferenceError.

Fix the bug by using the correct variable.

Author: strager

website/public/errors/error.ejs.html

@@ -95,7 +95,7 @@
           by following <code>wasm/README.md</code> and
           <code>website/README.md</code>.
         </p>
-        <p style="white-space: pre-line"><%= e %></p>
+        <p style="white-space: pre-line"><%= problems.join("\n") %></p>
       </div>
       <% } %> <%- errorDocument.toHTML() %>