Fix built in function file name

Author: Jiggly-Balls

zensical.toml

@@ -24,7 +24,7 @@ nav = [
       "python-tutorial/chapters/01-python-history.md",
       "python-tutorial/chapters/02-intro-to-variables.md",
       "python-tutorial/chapters/03-data-types-pt01.md",
-      "python-tutorial/chapters/04-built-in-functions-pt-1.md",
+      "python-tutorial/chapters/04-built-in-functions-pt01.md",
   ] },
   { "Resources" = [
     "resources/index.md",