PPA uses SHA1
It looks like your PPA is causing a security error message using the latest Ubuntu LTS (16.04). After apt-get update:
W: ftp://ftp.gajim.org/debian/dists/unstable/InRelease: Signature by key 95306A3F5430B830FE23ACEF838BC5151E5526DE uses weak digest algorithm (SHA1)
It would be great if you could update your PPA to use SSH2. See this link for more details: https://wiki.debian.org/Teams/Apt/Sha1Removal