Add tools/ to the style-checking path.

Test: Touch a Java file in tools/. `repo upload` gives warnings.
Change-Id: I381b01038d8a0c0e90817e383ca5323908fdd592
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 1084291..28aa06f 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -7,5 +7,4 @@
 
 [Hook Scripts]
 checkstyle_hook = ${REPO_ROOT}/prebuilts/checkstyle/checkstyle.py --sha ${PREUPLOAD_COMMIT}
-                  -fw updater_sample/
-
+                  --file_whitelist tools/ updater_sample/