Update snapcraft (#1347)

* Use python version instead of git describe

* Add snapcraft badge

Author: guilhem

README.md

@@ -3,6 +3,7 @@
 Keep your application settings in sync.
 
 [![Circle CI](https://circleci.com/gh/lra/mackup.svg?style=shield)](https://circleci.com/gh/lra/mackup)
+[![snapcraft](https://snapcraft.io/mackup/badge.svg)](https://snapcraft.io/mackup)
 
 ## Table of content
 

snap/snapcraft.yaml

@@ -1,6 +1,6 @@
 name: mackup
 version: git
-version-script: "git describe --tags"
+version-script: "python -c \"from mackup.constants import VERSION; print(VERSION)\""
 summary: Keep your application settings in sync
 description: |
   Back ups your application settings in a safe directory (e.g. Dropbox).