Update certificates.md

`openssl req -new -x509 -text -key client.key -out client.cert` creates a self-sign certificate but not a certificate request.

Signed-off-by: Wei-Ting Kuo <waitingkuo0527@gmail.com>

docs/sources/articles/certificates.md

@@ -45,7 +45,7 @@ Our example is set up like this:
 ## Creating the client certificates
 
 You will use OpenSSL's `genrsa` and `req` commands to first generate an RSA
-key and then use the key to create the certificate request.   
+key and then use the key to create the certificate.   
 
     $ openssl genrsa -out client.key 1024
     $ openssl req -new -x509 -text -key client.key -out client.cert