sshkey doesn't work

[guilhem]

Since 11b54be sshkey in cmdline doesn't work.
In fact "+" in json configuration became a " ".

here is line https://github.com/AcalephStorage/spriteful/blob/master/src/spriteful/spriteful.go#L146 and a quick and dirty fix https://github.com/guilhem/spriteful/commit/50e40a735aad26221518ecc06aef8043c12f3eb4