Fix full sync on Windows

From <https://docs.python.org/3.7/library/os.html#os.rename>:
> On Windows, if dst already exists, OSError will be raised even if
> it is a file.
...
> If you want cross-platform overwriting of the destination, use
> replace().

Thanks to kerry liu (https://github.com/hqzxjczx) for reporting this.

Fixes #32.

ankisyncd/full_sync.py

@@ -25,7 +25,7 @@ class FullSyncManager:
         # Overwrite existing db.
         col.close()
         try:
-            os.rename(temp_db_path, session.get_collection_path())
+            os.replace(temp_db_path, session.get_collection_path())
         finally:
             col.reopen()
             col.load()