bazelci.py: Add missing "import os"
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index d61b382..95c568f 100644
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -20,6 +20,7 @@
 import hashlib
 import json
 import multiprocessing
+import os
 import os.path
 import random
 import re