dev: rename default branch from master to main

Author: flavorjones

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ on:
     - cron: "0 5 * * 3" # At 05:00 on Wednesday # https://crontab.guru/#0_5_*_*_3
   push:
     branches:
-      - master
+      - main
     tags:
       - "*.*.*"
   pull_request:

README.md

@@ -221,7 +221,7 @@ For an example of rake tasks that support this style of invocation, visit https:
 
 ### Living on the edge: using weekly snapshots
 
-OCI images snapshotted from `master` are published weekly to Github Container Registry with the string "snapshot" in place of the version number in the tag name, e.g.:
+OCI images snapshotted from `main` are published weekly to Github Container Registry with the string "snapshot" in place of the version number in the tag name, e.g.:
 
 - `ghcr.io/rake-compiler/rake-compiler-dock-image:snapshot-mri-x86_64-linux`