One last fix for flit builds

It's `_version.py`, not `version.py` any more.

Author: DimitriPapadopoulos

tabulate/__init__.py

@@ -7,10 +7,10 @@
 from typing import Callable, Union
 
 try:
-    __version__ = _version("tabulate")
+    __version__ = _version("tabulate")  # installed package
 except _PackageNotFoundError:
     try:
-        from .version import version as __version__  # noqa: F401
+        from ._version import version as __version__  # editable / source checkout
     except ImportError:
         __version__ = "unknown"