Fix edit this page on GitHub link

Change master to main.

Author: danielledeleo

source/conf.py

@@ -32,7 +32,7 @@
 """.format(release_date)
 
 edit_on_github_project = 'nginx/unit-docs'
-edit_on_github_branch = 'master'
+edit_on_github_branch = 'main'
 
 exclude_patterns = ['include']
 suppress_warnings = ['misc.highlighting_failure']

source/exts/github.py

@@ -44,6 +44,6 @@ def setup(app):
     """Connects the extension to the app."""
 
     app.add_config_value("edit_on_github_project", "", True)
-    app.add_config_value("edit_on_github_branch", "master", True)
+    app.add_config_value("edit_on_github_branch", "main", True)
 
     app.connect("html-page-context", html_page_context)