Changed repo branch name from 'master' to 'main' in config.

_config.yml

@@ -83,7 +83,7 @@ parse:
 repository:
   url: https://gitlab.tudelft.nl/opentextbooks/NB1140/  # Online location of your book
   # path_to_book: docs  # Optional path to your book, relative to the repository root
-  branch: master  # Which branch of the repository should be used when creating links (optional)
+  branch: main  # Which branch of the repository should be used when creating links (optional)
 
 # HTML specific settings - see https://jupyterbook.org/en/stable/customize/config.html
 # Add GitHub / GitLab buttons to your book