Replace references to the master branch by main

Author: gollux

.github/CONTRIBUTING.md

@@ -6,9 +6,9 @@ uncontroversial and/or small), so that we can agree on the best way to implement
 it.
 
 We appreciate small commits that do one thing, but also that, when possible,
-each commit doesn't break the master branch. Please use your best judgement for
-the size of the commit according to these guidelines. If a commit breaks master,
-we at least require to push together all commits until master is fixed.
+each commit doesn't break the main branch. Please use your best judgement for
+the size of the commit according to these guidelines. If a commit breaks main,
+we at least require to push together all commits until main is fixed.
 
 We also appreciate a tidy history, so after you write all your code, consider
 tidying up the commits to reflect what you did at the end, which is usually a
@@ -18,7 +18,7 @@ how to make sure you don't introduce any).
 
 If your change involves more than one commit, please create a PR for each of
 them, unless for very small and obvious commits (read: fixing typos, comments, a
-few obvious lines), or unless some commit breaks master.
+few obvious lines), or unless some commit breaks main.
 
 During the review, please address all comments by creating one or more 'fixup'
 commits on top of the branch (no forced push). At the end, either you or one of

.github/ISSUE_TEMPLATE/Bug_report.md

@@ -32,7 +32,7 @@ If instead you have found a possible bug, please go ahead filing the issue using
 
 ### System Information
 
-**CMS version:** [master, or a specific version]
+**CMS version:** [main, or a specific version]
 **How was CMS installed:** [virtualenv, docker, ...?]
 **Postgres version:** [if relevant]
 **Distribution and version:** [if relevant]

README.md

@@ -4,7 +4,7 @@ Contest Management System
 Homepage: <http://cms-dev.github.io/>
 
 [![Build Status](https://github.com/cms-dev/cms/actions/workflows/main.yml/badge.svg)](https://github.com/cms-dev/cms/actions)
-[![Codecov](https://codecov.io/gh/cms-dev/cms/branch/master/graph/badge.svg)](https://codecov.io/gh/cms-dev/cms)
+[![Codecov](https://codecov.io/gh/cms-dev/cms/branch/main/graph/badge.svg)](https://codecov.io/gh/cms-dev/cms)
 [![Get support on Telegram](https://img.shields.io/badge/Questions%3F-Join%20the%20Telegram%20group!-%2326A5E4?style=flat&logo=telegram)](https://t.me/contestms)
 
 [🌍 Help translate CMS in your language!](https://cms-dev.oneskyapp.com/collaboration/project?id=392655)
@@ -28,7 +28,7 @@ Download
 which can be found already packaged at <http://cms-dev.github.io/>.**
 
 This git repository, which contains the development version in its
-master branch, is intended for developers and everyone interested in
+main branch, is intended for developers and everyone interested in
 contributing or just curious to see how the code works and wanting to
 hack on it.