fixing border style override

[lizlux]

The border: 1px solid; property was overriding the border color set in the mixin. This will let border color, width, and style be set independently of one another. Should fix the 1px height difference above and below primary buttons.

@Wikia/x-wing @vforge

[rogatty]

Please take a look at http://fandomdesignsystem.com/#/overview/contributing and:

• run npm run build to update the dist directory
• after this is merged to master, run npm run release-fix which will create the release and bump the package.json version
• update changelog on https://github.com/Wikia/design-system/releases

The change itself LGTM.

[lizlux]

Thanks @rogatty! Project is built.