I just want to put it here.
Add your domain on heroku via heroku CLI:
heroku domains:add www.your-domain.com
Go to Namecheap advance DNS settings and these records:
Type: CNAME Host: www Target: www.your-domain.com.herokudns.com. TTL: Automatic
Type: URL Redirect Record Host: @ Destination URL: http://www.your-domain.com TTL: Automatic Mask: Permanent (301)
Done!