Bump version to 0.6.8

README.md

-# lurch 0.6.7
+# lurch 0.6.8
 /lʊʁç/. In German, an Axolotl is a type of Lurch, which simply means 'amphibian'. This plugin brings _Axolotl_, by now renamed to _double ratchet_, to _libpurple_ applications such as [Pidgin](https://www.pidgin.im/) by implementing the [XEP-0384: OMEMO Encryption](https://xmpp.org/extensions/xep-0384.html). For a higher-level overview, see [the official OMEMO homepage](https://conversations.im/omemo/).
 
 (Plus I thought the word sounds funny.)

src/lurch.h

 #ifndef __LURCH_H
 # define __LURCH_H
 
-# define LURCH_VERSION "0.6.8-dev"
+# define LURCH_VERSION "0.6.8"
 # define LURCH_AUTHOR "Richard Bayerle <riba@firemail.cc>"
 
 #endif /* __LURCH_H */