Update docker-build.sh

change master to main

docker-build.sh

@@ -42,7 +42,7 @@ GIT_BRANCH=$(set -e && git rev-parse --abbrev-ref HEAD)
 # Get the default Git branch; default to master if it can't figure it out. You
 # may wish to edit this to some particular branch you want as the default; it
 # will be used to prewarm the build cache for new branches.
-GIT_DEFAULT_BRANCH=$(git rev-parse --abbrev-ref origin/HEAD || echo origin/master)
+GIT_DEFAULT_BRANCH=$(git rev-parse --abbrev-ref origin/HEAD || echo origin/main)
 GIT_DEFAULT_BRANCH=$(basename "${GIT_DEFAULT_BRANCH}")
 
 # Set two complete image names: