Don't zip toolchain/go/update_prebuilts.sh

Putting update_prebuilts.sh into into go.zip causes it to get copied
to prebuilts/go/linux-x86, where it doesn't work because the relative
path to the top of the tree is wrong.

Test: treehugger
Change-Id: I7c507db65fe1cc5e1b38f2750ae583fab9f08b85
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index 53463c2..09b1f9d 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -222,7 +222,7 @@
     )
     (
         cd ${GO_OUT}
-        zip -qryX go.zip *
+        zip -qryX go.zip * --exclude update_prebuilts.sh
     )
 fi