Deploy: use login shell for capistrano commands

On the server we were deploying to, the default non-interactive
environment for shell commands was bare. Using a login
shell ensures that at least .bashrc is loaded.

config/deploy.rb

@@ -16,6 +16,10 @@
 set :node_path, "/mnt/ebs/bin/node"
 
 default_run_options[:pty] = true
+# Use a login shell when executing commands so that
+# .bashrc and .bash_profile are loaded.
+set :default_shell, "sh -l"
+
 
 task :production do
   # :deployment variable should match task name