Fixed cli-table depencency and Litmus.getId() edge case

Hi,

i've finally found some spare time to integrate your plugin with my [boilerplate](https://github.com/dwightjack/grunt-email-boilerplate). 

Great work! Anyway I've noticed a couple of problems:

1) `cli-table` was in the `devDependencies` section, which is not downloaded when installing the plugin. I've moved it to `dependencies`.

2) I had an edge case with two existing tests having the same subject. By sending another test (again, with the  same subject), the `Litmus.getId()` was retrieving two test nodes. Ence the returned value was {testid1}{testid2}.
I've solved the issue changing the line:

```js
$matchedName.parent().children('id').text();
```

to
 
```js
$matchedName.first().parent().children('id').text();
```

I've already changed the patch version of the package and updated the readme.