Fix docs version (#880)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/source/conf.py

@@ -22,7 +22,7 @@
 HERE = osp.abspath(osp.dirname(__file__))
 ROOT = osp.dirname(osp.dirname(HERE))
 
-from traitlets import version_info
+from traitlets import __version__, version_info
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -82,7 +82,7 @@
 # The short X.Y version.
 version = ".".join(map(str, version_info[:2]))
 # The full version, including alpha/beta/rc tags.
-release = "__version__"
+release = __version__
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.