Make bazel start if ~/.cache doesn't exist yet

Change-Id: I0a9e8e7c88390ed909488d32cb958550f2986274
diff --git a/tools/bazel b/tools/bazel
index a691066..d305cf5 100755
--- a/tools/bazel
+++ b/tools/bazel
@@ -33,7 +33,7 @@
 
 # Creating might fail if another invocation is racing us.
 if [[ ! -d "${DOWNLOAD_DIR}" ]]; then
-  mkdir "${DOWNLOAD_DIR}" || true
+  mkdir -p "${DOWNLOAD_DIR}" || true
 fi
 if [[ ! -d "${DOWNLOAD_DIR}" ]]; then
   echo "Failed to create ${DOWNLOAD_DIR}" >&2