Rename default branch to main

CONTRIBUTING.md

@@ -31,8 +31,8 @@ None of these is essential for a pull request, but they will all help
   than cosmetic changes).
 - Add some Javadocs
 - Add unit tests that covers and new or modified functionality
-- Whenever possible, please rebase your branch against the current master (or other
-  target branch in the main project).
+- Whenever possible, please rebase your branch against the current main (or other
+  target branch in the project).
 * When writing a commit message please follow [these conventions][3]. Also, if you are
   fixing an existing issue please add `Fixes gh-nnn` at the end of the commit message
   (where nnn is the issue number).

docs/build.gradle

@@ -26,6 +26,6 @@ asciidoctor {
 		include 'index.adoc'
 	}
 	attributes	'revnumber': project.version,
-				'branch-or-tag': project.version.endsWith('SNAPSHOT') ? 'master': "v${project.version}"
+				'branch-or-tag': project.version.endsWith('SNAPSHOT') ? 'main': "v${project.version}"
 	inputs.files(sourceSets.test.java)
 }