[omemo] Update manifest.ini & CHANGELOG

omemo/CHANGELOG

+2.6.74 / 2020-02-14
+- Switch to 12 byte IV
+
 2.6.73 / 2020-01-19
 - Don't show warning for Key Transport messages
 

omemo/manifest.ini

 [info]
 name: OMEMO
 short_name: omemo
-version: 2.6.73
+version: 2.6.74
 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, detailed in the installation instructions for your system in the GitHub wiki.
 authors: Bahtiar `kalkin-` Gadimov <bahtiar@gadimov.de>
  Daniel Gultsch <daniel@gultsch.de>