pw_env_setup: Sort missing submodules

Change-Id: Idb7485d2ad94629487e9e2b2e34cbc7f6dc9ed45
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97903
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/pw_env_setup/py/pw_env_setup/env_setup.py b/pw_env_setup/py/pw_env_setup/env_setup.py
index ab6d2dd..8900943 100755
--- a/pw_env_setup/py/pw_env_setup/env_setup.py
+++ b/pw_env_setup/py/pw_env_setup/env_setup.py
@@ -345,7 +345,7 @@
                 file=sys.stderr)
             print('', file=sys.stderr)
 
-            for miss in missing:
+            for miss in sorted(missing):
                 print('    git submodule update --init {}'.format(miss),
                       file=sys.stderr)
             print('', file=sys.stderr)