[damned-lies] Add missing self param to RepoBase.exists

[Claude Paroz <claudep src gnome org>]

commit 22109e6db65dab2ae66053a2ffcebab00a20a88b
Author: Claude Paroz <claude 2xlibre net>
Date:   Sat Oct 6 17:40:25 2018 +0200

    Add missing self param to RepoBase.exists

 stats/repos.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/stats/repos.py b/stats/repos.py
index 6913a98e..bc8f09df 100644
--- a/stats/repos.py
+++ b/stats/repos.py
@@ -13,7 +13,7 @@ class RepoBase:
     def __init__(self, branch):
         self.branch = branch
 
-    def exists():
+    def exists(self):
         return os.access(str(self.branch.co_path), os.X_OK | os.W_OK)
 
     def checkout(self):