[cipd wrapper] add arm64 as a valid machine

Change-Id: I63bc5fdb28731a4006f179214a845168225ffa8c
diff --git a/cipd b/cipd
index cdab3b4..57d1652 100755
--- a/cipd
+++ b/cipd
@@ -31,6 +31,9 @@
   arm*)
     readonly HOST_ARCH="${HOST_ARCH}"
     ;;
+  aarch64)
+    readonly HOST_ARCH="arm64"
+    ;;
   *86)
     readonly HOST_ARCH=386
     ;;