findmissing: Add v5.8 to list of stable branches

BUG=None
TEST=Run tool and verify that 5.8 is supported

Change-Id: Iab4ca19d77f0cef0fba19adf8f821b90e8e6dec0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2364469
Reviewed-by: Curtis Malainey <cujomalainey@chromium.org>
Commit-Queue: Guenter Roeck <groeck@chromium.org>
Tested-by: Guenter Roeck <groeck@chromium.org>
diff --git a/contrib/findmissing/common.py b/contrib/findmissing/common.py
index feb71c9..3beecd8 100755
--- a/contrib/findmissing/common.py
+++ b/contrib/findmissing/common.py
@@ -33,7 +33,7 @@
 
 # Order BRANCHES from oldest to newest
 CHROMEOS_BRANCHES = ['4.4', '4.14', '4.19', '5.4']
-STABLE_BRANCHES = ['4.4', '4.9', '4.14', '4.19', '5.4', '5.7']
+STABLE_BRANCHES = ['4.4', '4.9', '4.14', '4.19', '5.4', '5.7', '5.8']
 
 UPSTREAM_START_BRANCH = 'v%s' % CHROMEOS_BRANCHES[0]