git_pull: Prevent plugin from always restarting hass.io even if nothing has changed (#205)

* Prevent git module from always restarting hass.io

`git diff-tree -r --name-only --no-commit-id 'HEAD@{1}' HEAD)` always shows a difference. Getting the commit id prior to pulling is easy and comparing it to the one after pulling makes sure, that checking and restart is only done if ids have changed.

* Forgot to get the OLD_COMMIT id

* Better sorting and further comments

* Pleasing the linter

* Update config.json

git_pull/config.json

@@ -1,6 +1,6 @@
 {
   "name": "Git pull",
-  "version": "2.1",
+  "version": "2.2",
   "slug": "git_pull",
   "description": "Simple git pull to update the local configuration",
   "url": "https://home-assistant.io/addons/git_pull/",