fetch-bundled_gems.rb: Fixed the position of -c

tool/fetch-bundled_gems.rb

@@ -17,7 +17,7 @@ else
   puts "retrieving #{n} ..."
   system(*%W"git clone #{u} #{n}") or abort
 end
-checkout = %w"git checkout -c advice.detachedHead=false"
+checkout = %w"git -c advice.detachedHead=false checkout"
 unless system(*checkout, v.sub(/\A(?=\d)/, 'v'), chdir: n)
   unless /\A\d/ =~ v and system(*checkout, v, chdir: n)
     abort