Fix _try_directories in horizons.utils.platform

`os.path.join()` joins its arguments and doesn't take the paths from a
list/tuple.

> TypeError: join() argument must be str or bytes, not 'tuple'

horizons/util/platform.py

@@ -66,7 +66,7 @@ def _try_directories(paths, default=None):
 	# (lists could also be tuples of course)
 	for parts in paths:
 		if all(parts):
-			return os.path.join(parts)
+			return os.path.join(*parts)
 	return default