link_to event/staff/proposal page from admin/user

because event/proposal page can be viewed from the submitters only, and
thus it usually ends up with "You are not an invited speaker for the
proposal you are trying to access." error.

Author: amatsuda

app/views/admin/users/show.html.haml

@@ -24,7 +24,7 @@
           - talks.each do |proposal|
             %tr
               %td= link_to event.name, event
-              %td= link_to proposal.title, [proposal.event, proposal]
+              %td= link_to proposal.title, [proposal.event, :staff, proposal]
               %td= proposal.state
               %td= truncate(proposal.abstract, length: 80)