Updating default adium installed to 1.5.7

A version bump to [1.5.7][1]

[Changelog][2] includes some fixes for potential SSL weaknesses

[1]: https://adium.im/blog/2013/07/adium-1-5-7-released/
[2]: https://trac.adium.im/wiki/AdiumVersionHistory#Version1.5.7722013