If an alias uses command, modify it to not do that

[daniellandau]

First of all thank you for making this tool, this is great!

I did hit a snag while testing it, in that it didn't actually sandbox ls in my environment. I thought it might have been something with the precmds and accept-lines I already had, but instead it turned out to be an issue with the ls alias I get from using the GRML ZSH config. It defines the alias as:

alias ls="command ls ${ls_options:+${ls_options[*]}}"

I haven't found any adverse effects from the the change in this PR that strips the command from any alias.