Repository#path_to_repo should always return absolute path

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/repository.rb

@@ -10,8 +10,11 @@ class Repository
     nil
   end
 
+  # Return absolute path to repository
   def path_to_repo
-    @path_to_repo ||= File.join(Gitlab.config.gitlab_shell.repos_path, path_with_namespace + ".git")
+    @path_to_repo ||= File.expand_path(
+      File.join(Gitlab.config.gitlab_shell.repos_path, path_with_namespace + ".git")
+    )
   end
 
   def exists?