Fix bug which was causing custom scripts to never be loaded

[victorquinn]

As previously written, the scripts variable was set to the docpress metadata which is an object. For example, this is what I had in my repo:

let scripts = ms.metadata()

// Now scripts is:
// {
//   docs: 'docs',
//   dist: '_docpress',
//   scripts: [ 'chance.js', 'analytics.js' ],
//   github: 'chancejs/chancejs',
//   plugins: { 'docpress-core': {}, 'docpress-base': {} }
// }

As a result, checking a few lines lower (on line 126) if scripts is an Array would always fail and no scripts would ever be loaded. I'm not sure how this ever worked.

My fix ensures it finds the scripts key within the metadata and assigns that to the scripts variable so it should properly reference scripts added to the docpress.json or in the package.json to the docpress section.

[coveralls]

Coverage remained the same at 82.353% when pulling decae8c on victorquinn:master into fce4ce1 on docpress:master.

[knownasilya]

Thanks @victorquinn