Issue title: Not recursive?
 Issue body: If we have a scenario where

File 1:

``` javascript
//= require myfile.js
//= require someotherfile.js
//= require ../somemodule/main.js
```

somemodule/main.js:

``` javascript
//= require something.js
//= require blah.js
```

We're not going to get all the files from `somemodule/main.js` are we?

 Comments: 
 Comment 0: +1
can't use such relative paths

 Comment 1: +1 I'm looking for a gulp version of this : https://github.com/vanetix/grunt-includes and recursivity is the only thing missing for me

 Comment 2: For those looking for this kind of functionality, you might want to look into [Mincer](https://github.com/nodeca/mincer)

 Comment 3: :+1: for this. Not a fan of `//= require_tree`, so being able to do some sort of selective recursion would be nice.

 Comment 4: Just submitted a pull request that supports this, and globbing.

 Comment 5: @scottmas :100: 

 Comment 6: @scottmas Nice! Hope your PR will be merged soon! :+1: 

 Comment 7: I can see that this has been merged, but for me this isn't working. I am using Gulp 3.9 and the latest version of gulp-include available. I just get `//=include ../components/setUtils.js` in the source code after compile.

My path through:

`index.js -> [require] ../utils/pluginExists.js -> [require] ../components/setUtils.js`

Am I doing something wrong here?
{'source': 'GithubIssues', 'repo_name_with_owner': 'wiledal/gulp-include', 'issue_id': 30074666, 'repo_stars': 159.0}