[omemo] Update CHANGELOG & manifest.ini

omemo/CHANGELOG

+1.2.8 / 2017-10-07
+- Bug fixes
+
 1.2.7 / 2017-08-26
 - Query only the most recent PEP item
 

omemo/manifest.ini

 [info]
 name: OMEMO
 short_name: omemo
-version: 1.2.7
+version: 1.2.8
 description: OMEMO is an XMPP Extension Protocol (XEP) for secure multi-client end-to-end encryption based on Axolotl and PEP. You need to install some dependencies. For install instructions, see the GitLab Wiki.
 authors: Bahtiar `kalkin-` Gadimov <bahtiar@gadimov.de>
  Daniel Gultsch <daniel@gultsch.de>