[omemo] Reference python 3 dependencies

omemo/omemoplugin.py

@@ -41,8 +41,8 @@ from omemo.xmpp import DevicelistPEP
 from omemo.gtk.key import KeyDialog
 from omemo.gtk.config import OMEMOConfigDialog
 
-CRYPTOGRAPHY_MISSING = 'You are missing Python-Cryptography'
-AXOLOTL_MISSING = 'You are missing Python-Axolotl or use an outdated version'
+CRYPTOGRAPHY_MISSING = 'You are missing Python3-Cryptography'
+AXOLOTL_MISSING = 'You are missing Python3-Axolotl or use an outdated version'
 PROTOBUF_MISSING = 'OMEMO cant import Google Protobuf, you can find help in ' \
                    'the GitHub Wiki'
 ERROR_MSG = ''