Escape backticks and $ in saved environment so they are preseved from one save to the next

This is to preserve command replacement in things like the logrotate command for chore. The value is 

```sh
su - webuser -c 'kill -s USR1 \`/opt/apps/tapjoyserver/server/chore_master_pid.rb\`'
```

If we source that and then save it again the backticks get unescaped and then excuted on save. The sed command here keeps them escaped so the value is the same if we source the environment we saved and source and save and source and save etc.

@liamneesonsarm @gerbercj @andyleclair