Add a global `Y` zsh alias to conditionally run a command

Let's say you're running a command. Let's call it `bundle install`. And
you're being wicked fast developer. And you decide you want to go ahead
and type the next command before this one is finished. But actually if
that command failed it wouldn't be good for the next one to run. Let's
call this command `git commit -am yolo && git push -f`.

Well simple you say, just chain the commands with `&&`. But, what if I
forgot?

Enter `Y`. Preface your next command with it and it will prevent your
next command from running if your last command didn't `exit 0`.

Example:

```
$ bundle install
Fetching gem metadata from https://rubygems.org/...
Y git commit -am yolo && git push -f
Couldn't satisfy all the gems versions. (exit != 0)
$
```

Notice `git` didn't run? Yeah thanks `Y`, I shall live another day.