Update outdated branch URLs

.github/config.yml

@@ -8,7 +8,7 @@ newIssueWelcomeComment: >
   (Image: CC-BY license, The Turing Way Community, & Scriberia. Zenodo. http://doi.org/10.5281/zenodo.3332808)
   Hi there, and welcome to the DataLad Handbook! :orange_book: :wave:
   Thank you for filing an issue. We're excited to have your input and welcome your idea! :blush:
-  If you haven't done so already, please make sure you check out our [Code of Conduct](https://github.com/datalad-handbook/book/blob/master/CODE_OF_CONDUCT.md).
+  If you haven't done so already, please make sure you check out our [Code of Conduct](https://github.com/datalad-handbook/book/blob/main/CODE_OF_CONDUCT.md).
 
 # Configuration for new-pr-welcome - https://github.com/behaviorbot/new-pr-welcome
 
@@ -27,4 +27,4 @@ firstPRMergeComment: >
   (Image: CC-BY license, The Turing Way Community, & Scriberia. Zenodo. http://doi.org/10.5281/zenodo.3332808)
   Congrats on merging your first pull request! :tada:
   The DataLad Handbook team appreciates your contribution greatly, and we want to say thanks! :sparkling_heart:
-  Now go ahead and share your first merge with your colleagues, you got yourself this brag right! :smile: :gift:
+  Now go ahead and share your first merge with your colleagues, you got yourself this brag right! :smile: :gift:

README.md

@@ -50,7 +50,7 @@ under the following terms:
 2) **ShareAlike** — If you remix, transform, or build upon the material, you must distribute your
  contributions under the same license as the original.
 
-<img src="https://raw.githubusercontent.com/datalad-handbook/book/master/artwork/logo.svg?sanitize=true" width="200" height="400">  
+<img src="https://raw.githubusercontent.com/datalad-handbook/book/main/artwork/logo.svg?sanitize=true" width="200" height="400">
 
 ## Contributors ✨
 

docs/OHBMposter.rst

@@ -12,7 +12,7 @@ Here you can find the poster about the DataLad Handbook, presented at the `2020
    Click on the image below to obtain a PDF version of it.
 
    .. figure:: artwork/src/OHBM_2020.png
-      :target: https://github.com/datalad-handbook/book/raw/master/artwork/OHBM_2020.pdf
+      :target: https://github.com/datalad-handbook/book/raw/main/artwork/OHBM_2020.pdf
 
 
 .. only:: latex
@@ -21,4 +21,4 @@ Here you can find the poster about the DataLad Handbook, presented at the `2020
       :width: 80%
 
       A high-resolution version is available for download
-      at https://github.com/datalad-handbook/book/raw/master/artwork/OHBM_2020.pdf
+      at https://github.com/datalad-handbook/book/raw/main/artwork/OHBM_2020.pdf

docs/basics/101-136-cheatsheet.rst

@@ -13,7 +13,7 @@ DataLad cheat sheet
    sections are linked to chapters or technical docs.
 
    .. figure:: ../artwork/src/datalad-cheatsheet_p1.png
-      :target: https://github.com/datalad-handbook/artwork/raw/master/src/datalad-cheatsheet.pdf
+      :target: https://github.com/datalad-handbook/artwork/raw/main/src/datalad-cheatsheet.pdf
 
 .. only:: latex
 
@@ -21,4 +21,4 @@ DataLad cheat sheet
       :width: 80%
 
       A high-resolution version of this cheatsheet is available for download
-      at https://github.com/datalad-handbook/artwork/raw/master/src/datalad-cheatsheet.pdf
+      at https://github.com/datalad-handbook/artwork/raw/main/src/datalad-cheatsheet.pdf