AppleTLS: correctly define kTLSProtocol13

src/AppleTLSSession.cc

@@ -55,7 +55,10 @@ namespace {
 #if !defined(__MAC_10_8)
 static const SSLProtocol kTLSProtocol11 = 7;
 static const SSLProtocol kTLSProtocol12 = 8;
-static const SSLProtocol kTLSProtocol13 = 13;
+#endif
+
+#if !defined(__MAC_10_13)
+static const SSLProtocol kTLSProtocol13 = 10;
 #endif
 
 #ifndef CIPHER_NO_DHPARAM