doc: change "OCSP Request" to "OCSP request"

PR-URL: #42582
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>

Author: tniessen

doc/api/tls.md

@@ -605,7 +605,7 @@ no OCSP response.
 
 Calling `callback(err)` will result in a `socket.destroy(err)` call.
 
-The typical flow of an OCSP Request is as follows:
+The typical flow of an OCSP request is as follows:
 
 1. Client connects to the server and sends an `'OCSPRequest'` (via the status
    info extension in ClientHello).