Image on homepage doesn't use non-ssl source

The image for bitcore.io was sourced from `http://bitcore.io/images/logo.svg`, causing errors with ssl due to loading a non-ssl resource.

Before
`a.bitcore{background-image:url(http://bitcore.io/images/logo.svg);background-size:80px;width:30%}`
After
`a.bitcore{background-image:url(/img/logo.svg);background-size:80px;width:30%}`

This was a simple matter of running `grunt compile`. There were also a couple of javascript files that were modified by compiling, but since they were unrelated to this issue (non-ssl resources) I left the minified versions unchanged. Might be worth having a look into.