Delete files in :shared_files before creating a symlink (fixes #452)

:shared_files like database.yml / secrets.yml are often checked in the repo for development and should be overwritten by the link to the shared file under mina deployment.

tasks/mina/deploy.rb

@@ -27,6 +27,7 @@
     end
 
     fetch(:shared_files, []).each do |linked_path|
+      command %{rm -f "./#{linked_path}"}
       command %{ln -s "#{fetch(:shared_path)}/#{linked_path}" "./#{linked_path}"}
     end
   end