Add ability to use multiple glob patterns

gulp accepts multiple glob patterns, such as:

```js
gulp.src(['*src/*.css', 'vendor/*.css'])
```

This feature is very useful, but this plugin doesn't have that, currently.

So I introduced [multimatch](https://github.com/sindresorhus/multimatch) to accept multiple glob patterns.
After merging this PR, we can use this plugin as below:

```js
var gulp = require('duo-gulp');
var duo = Duo(root).entry(entry);
var uncss = require('gulp-uncss');

duo.use(gulp(['src/*.css', 'vendor/*.css'], uncss)());
```