herokuで運営しているサイトをhttps://にする設定

Herokuを使って独自ドメインでサイトを公開しているのですが、そのサイトをhttps://に変更したいのですが、

http://threetreeslight.com/post/48600890187/heroku%E3%81%B8%E3%83%87%E3%83%97%E3%83%AD%E3%82%A4%E3%81%97%E3%81%A6%E3%81%84%E3%82%8B%E3%82%B5%E3%83%BC%E3%83%93%E3%82%B9%E3%81%AEssl%E8%A8%AD%E5%AE%9A
を参考にして進めていったのですが、
【追記】
このサイトと同じく証明書はRapid-SSL.jpで取得しました

進行方法

$  openssl genrsa -des3 -out server.orig.key 2048
Generating RSA private key, 2048 bit long modulus
.........................................+++
......+++
e is 65537 (0x10001)
Enter pass phrase for server.orig.key:
Verifying - Enter pass phrase for server.orig.key:

$ openssl rsa -in server.orig.key -out server.key
Enter pass phrase for server.orig.key: 任意のパスワード入力
writing RSA key 任意のパスワード再入力

$ openssl req -new -key server.key -out server.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:JP
State or Province Name (full name) []:Tokyo
Locality Name (eg, city) [Default City]:Shinagawa
Organization Name (eg, company) [Default Company Ltd]:hogehoge
Organizational Unit Name (eg, section) []:
Common Name (eg, your name or your server's hostname) []:www.hogehoge.com
Email Address []:hogehoge@gmail.com

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:入力せず
An optional company name []: 入力せず

$ vim server.crt
SSL証明書、中間証明書を入力

$ heroku addons:add ssl
WARNING: `heroku addons:add` has been deprecated. Please use `heroku addons:create` instead.
Creating ssl-closed-9022... done, ($20.00/month)
Adding ssl-closed-9022 to cosp-log... done
Next add your certificate with `heroku certs:add PEM KEY`.
Use `heroku addons:docs ssl` to view documentation.

$ heroku certs:add --app hoge_app server.crt server.key
Resolving trust chain... failed
 !    No key found that signs the certificate.