libsodium: 1.0.3 -> 1.0.6

[joachifm]

See https://github.com/jedisct1/libsodium/releases/tag/1.0.4

Builds successfully for me, all tests pass, nothing scary in the changelog, as far as I can tell.

[joachifm]

The travis failure is unrelated:

building path(s) ‘/nix/store/8n9xkwpdx7kqsicjx42kq26bys8a3gv2-0.5.2.zip’
 57 8703k   57 5029k    0     0   558k      0  0:00:15  0:00:09  0:00:06  607k
trying https://github.com/rescrv/po6/archive/releases/0.5.2.zip
output path ‘/nix/store/8n9xkwpdx7kqsicjx42kq26bys8a3gv2-0.5.2.zip’ should have sha256 hash
‘14g3ichshnc4wd0iq3q3ymgaq84gjsbqcyn6lri7c7djgkhqijjx’, instead has ‘17grzkh6aw1f68qvkhivbb6vwbm6jd41ysbfn88pypf5lczxrxly’