SSL: X509 was made opaque in OpenSSL 1.1.0.

To increment reference counters we now use newly introduced X509_up_ref()
function.

src/event/ngx_event_openssl_stapling.c

diff --git a/src/event/ngx_event_openssl_stapling.c b/src/event/ngx_event_openssl_stapling.c
index 3f2351c..5322b1b 100644
--- a/src/event/ngx_event_openssl_stapling.c
+++ b/src/event/ngx_event_openssl_stapling.c
@@ -285,7 +285,11 @@
     for (i = 0; i < n; i++) {
         issuer = sk_X509_value(chain, i);
         if (X509_check_issued(issuer, cert) == X509_V_OK) {
+#if OPENSSL_VERSION_NUMBER >= 0x10100001L
+            X509_up_ref(issuer);
+#else
             CRYPTO_add(&issuer->references, 1, CRYPTO_LOCK_X509);
+#endif
 
             ngx_log_debug1(NGX_LOG_DEBUG_EVENT, ssl->log, 0,
                            "SSL get issuer: found %p in extra certs", issuer);