Fix grammar error in SSL_CTX_set_min_proto_version

CLA: trivial
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1762)

doc/ssl/SSL_CTX_set_min_proto_version.pod

@@ -34,7 +34,7 @@ B<DTLS1_2_VERSION> for DTLS.
 
 =head1 RETURN VALUES
 
-Both functions return 1 on success and 0 on failure.
+These functions return 1 on success and 0 on failure.
 
 =head1 NOTES