moblab_config: bump stable version

BUG=chromium:674762
TEST=autotest artifacgts exist for both cyan and samus for this image
version in gs.

Change-Id: I342a574399f480a6d828165d1d99781649feaa12
Reviewed-on: https://chromium-review.googlesource.com/420414
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Kevin Cheng <kevcheng@chromium.org>
diff --git a/moblab_config.ini b/moblab_config.ini
index 815bbf8..f660f5f 100644
--- a/moblab_config.ini
+++ b/moblab_config.ini
@@ -24,4 +24,4 @@
 # In moblab, this paramater is empty and uses the image bucket by default.
 results_storage_server:
 cts_results_server:
-stable_cros_version: R53-8480.0.0
+stable_cros_version: R55-8872.67.0