Support main branch for syntax_suggest

tool/sync_default_gems.rb

@@ -547,6 +547,12 @@ end
 def update_default_gems(gem, release: false)
 
   author, repository = REPOSITORIES[gem.to_sym].split('/')
+  default_branch = case gem
+                  when 'syntax_suggest'
+                    "main"
+                  else
+                    "master"
+                  end
 
   puts "Update #{author}/#{repository}"
 
@@ -572,8 +578,8 @@ def update_default_gems(gem, release: false)
       last_release = `git tag`.chomp.split.delete_if{|v| v =~ /pre|beta/ }.last
       `git checkout #{last_release}`
     else
-      `git checkout master`
-      `git rebase origin/master`
+      `git checkout #{default_branch}`
+      `git rebase origin/#{default_branch}`
     end
   end
 end