fix issues with rbenv:load

[devvmh]

I put the rbenv:load call in my deploy.rb inside an in_path call like so:

task :environment do
  in_path(fetch(:deploy_to)) do
    invoke :'rbenv:load'
  end
end

This caused a zsh parse error (and I'm assuming bash would have the same problem) because the shell script came out as:

(cd /deploy/path/current && echo "-----> Loading rbenv" && export RBENV_ROOT='$HOME/.rbenv' && export PATH='$HOME/.rbenv/bin:$PATH' &&  (
    if ! which rbenv >/dev/null; then
      echo "! rbenv not found"
      echo "! If rbenv is installed, check your :rbenv_path setting."
      exit 1
    fi )
   && eval "$(rbenv init -)")

[devvmh]

Ooh, and these single quotes are causing issues regardless of using in_path