Fix: rubocop-friendly event handler generator.

Author: dblock

lib/slack/real_time/api/templates/event_handler.erb

@@ -4,5 +4,5 @@
 <% if hook %>
 <%= hook %>
 <% else %>
-          # on :<%= name %> do |data|
+        # on :<%= name %> do |data|
 <% end %>