Fix syntax in robots.txt

We added the `user_id` rule in commit edaf420f5. To be honest, I'm not
sure what we meant, since I haven't found URLs containing the user id.

So we're treating it as if it was a typo and we wanted to do the same
thing we did with other parameters.

app/views/robots/index.text.erb

@@ -12,6 +12,6 @@ Disallow: /*?*order
 Disallow: /*?*search
 Disallow: /*?*locale-switcher
 Disallow: /*?*filter
-Disallow: user_id
+Disallow: /*?*user_id
 
 Sitemap: <%= "#{root_url}#{Tenant.path_with_subfolder("sitemap.xml")}" %>