[roll] Roll fuchsia [assembly] Output relative paths to images.json

Put relative paths into images.json when doing out-of-tree assembly.

Original-Bug: 103261
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/698144
Original-Revision: f3d098f357efe37acd60b0a02c543e7db20d5cd0
GitOrigin-RevId: 2f3ff45d0953bb5f77648baf18ad2355c574da85
Change-Id: If46cf2ce5769dd44e9b4a00aec0dd9260d0ffab7
diff --git a/stem b/stem
index 0a59f21..dcdb788 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="7c60da13792bf26ca503ecd4767e4f3d6076a639"/>
+             revision="f3d098f357efe37acd60b0a02c543e7db20d5cd0"/>
   </projects>
   <hooks>
     <hook name="install-environment"