Update configuration.md

Fix minimal typo, tripping me (and most likely others) during setup. (e.g. #854)

docs/configuration.md

@@ -30,9 +30,9 @@ Specifies the type of backend to use and its location. More information
 on the format used can be found on [the SQLAlchemy
 documentation](http://docs.sqlalchemy.org/en/latest/core/engines.html#database-urls).
 
--   **Default value:** `sqlite:///tmp/ihatemoney.db`
+-   **Default value:** `sqlite:////tmp/ihatemoney.db`
 -   **Production value:** Set it to some path on your disk. Typically
-    `sqlite:///home/ihatemoney/ihatemoney.db`. Do *not* store it under
+    `sqlite:////home/ihatemoney/ihatemoney.db`. Do *not* store it under
     `/tmp` as this folder is cleared at each boot.
 
 For example, if you're using MariaDB, use a configuration similar to