OSX Build: Fixed generated filename for El Capitan
OSX Build: Fixed generated filename for El Capitan

Our convention for the legacy El Capitan build was the
-macosx-elcapitan.dmg (so that it sorts after the plain -macosx.dmg).

The build script had it reversed as -elcapitan-macos.dmg (and it sorted
first, making it more likely users would just download that one).

This has now been fixed.

fyookball/electrum,fyookball/electrum,fyookball/electrum