Use zip for foundation

To avoid the recurrent error in travis with Foundation:

    [exec]   - Installing zurb/foundation (v4.3.2)
    [exec]     Cloning a2a39011003b6ade6cb522a206449070b8b8ccd3
    [exec]     a2a39011003b6ade6cb522a206449070b8b8ccd3 is gone (history
was rewritten?)
    [exec]     Failed to download zurb/foundation from source: Failed to
execute git checkout 'a2a39011003b6ade6cb522a206449070b8b8ccd3' && git
reset --hard 'a2a39011003b6ade6cb522a206449070b8b8ccd3'
    [exec]
    [exec] fatal: reference is not a tree:
a2a39011003b6ade6cb522a206449070b8b8ccd3
    [exec]
    [exec]     Now trying to download from dist
    [exec]   - Installing zurb/foundation (v4.3.2)
    [exec]     Downloading: connection...
    [exec]
    [exec]
    [exec]
    [exec]   [Composer\Downloader\TransportException]
    [exec]   Could not authenticate against github.com