fixed invalid doc example for cmd.run

the example given in the documentation is invalid with the ``!`` mark, but it is also a bit confusing. I hope this helps!

```bash
$ echo "changed=yes comment="something's changed!" whatever=123"
                                                         
quote> 
```

This works:
```bash
$ echo "changed=yes comment='something has changed' whatever=123"                                                        

changed=yes comment='something has changed' whatever=123
```

From reviewing the [documentation](https://salt.readthedocs.org/en/latest/ref/states/all/salt.states.cmd.html), it looks like the entire line needs to be a string? I think I got this right...
> the stdout must be either in JSON or its last non-empty line 
> must be a string of key=value pairs delimited by spaces
> (no spaces on the sides of =).