Rename Magenta to Zircon

Change-Id: Ia8c516ca4f3acc80fd3eae836dce454d1a4a5c36
diff --git a/src/core/lib/iomgr/port.h b/src/core/lib/iomgr/port.h
index 63ba365..8a2f889 100644
--- a/src/core/lib/iomgr/port.h
+++ b/src/core/lib/iomgr/port.h
@@ -135,7 +135,7 @@
 #define GRPC_HAVE_IFADDRS 1
 #define GRPC_HAVE_IPV6_RECVPKTINFO 1
 #define GRPC_HAVE_IP_PKTINFO 1
-// Magenta does not support the MSG_NOSIGNAL flag since it doesn't support
+// Zircon does not support the MSG_NOSIGNAL flag since it doesn't support
 // signals.
 #undef GRPC_HAVE_MSG_NOSIGNAL
 #define GRPC_HAVE_UNIX_SOCKET 1