Fixing dependencies parameter on sensu_check type

It appears that currently the sensu_check dependencies parameter is treating a given array as a string.  

With the following configuration

```
sensu::check { 'mycheck':
        command      => '/etc/sensu/plugins/mycommand',
        interval     => 120,
        standalone   => false,
        subscribers  => ['mygroup'],
        dependencies => ['my-first-check', 'my-second-check']
}
```

Will produce a configuration file which dependencies section looks like:
```
"dependencies": [
  "my-first-test"
],
```
Adding this change seems to fix the issue.  I am fairly new to this so if there is a better way to fix this please let me know.