Update Safari for iOS logo

Make logo better reflect the official one.
Add Safari 8 logo

Safari 8 (which is bundled with OS X Yosemite) comes with
a new logo, different from the one used by previous versions.

Ref: https://www.youtube.com/watch?v=w87fOAG8fjk&t=26m58s
Close: alrra/browser-logos#46