ssl: use TLS_method() instead of SSLv23_method() for LibreSSL

LibreSSL 2.2.2 introduced TLS_method(), but with different semantics
from OpenSSL: TLS_method() enabled TLS >= 1.0 while SSLv23_method()
enabled all available versions, which included SSL 3.0 in addition.

However, LibreSSL 2.3.0 removed SSL 3.0 support completely and now
TLS_method() and SSLv23_method() are equivalent.

ext/openssl/ossl_ssl.c

@@ -81,7 +81,7 @@ ossl_sslctx_s_alloc(VALUE klass)
     VALUE obj;
 
     obj = TypedData_Wrap_Struct(klass, &ossl_sslctx_type, 0);
-#if OPENSSL_VERSION_NUMBER >= 0x10100000 && !defined(LIBRESSL_VERSION_NUMBER)
+#if OPENSSL_VERSION_NUMBER >= 0x10100000 || defined(LIBRESSL_VERSION_NUMBER)
     ctx = SSL_CTX_new(TLS_method());
 #else
     ctx = SSL_CTX_new(SSLv23_method());