Dont lint html commented scripts

cf issue #11
#### Supported use cases 
* commented script tags :

  ```html
<!--
I start writting documentation (let's say in markdown)
Now I want to include a example of use:

    <tags> </tags>..
    <script>
        the example of script, with errors
    </script>
@element my-elem
-->
<polymer-element name="my-elem" .... >
...
```
  :arrow_right: **won't** raise an error
* html comments
  
  ```html
<script>
    (function() {
        var trapStarts = "<!--";
        var inTheTrap = "bar" // should be linted and raise a error
        var trapEnds = "-->";
    }(this));
</script>
```
  :arrow_right: **will** raise an error