[whispersystems] Source from 3.20.4

[Johan Wevers]

Hello,

I saw that 3.20.4 was released but the Github source is still at 3.20.3
+ some updates
(https://github.com/WhisperSystems/Signal-Android/commit/8d44a145f02f34f30983405a42e9d4a39d2d18de).
Since one of those updates is to make a string translatable I'm not sure
if 3.20.4 is just current Github + a version bump. Since I'm building my
own version I'd like to know.