[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

nbconvert/exporters/slides.py

@@ -134,6 +134,7 @@ def _reveal_url_prefix_default(self):
             )
             return self.config.RevealHelpPreprocessor.url_prefix
         return "https://unpkg.com/reveal.js@4.0.2"
+
     reveal_theme = Unicode(
         "simple",
         help="""