Fix stripping of executable bit from artifacts

- Well, turns out KOKORO_GFILE_DIR is inside KOKORO_ARTIFACTS_DIR, which
means we have directories in there. Setting those -x makes them
unreadable, and syncing back artifacts freaks out.

Change-Id: Ifcf673442714509e4994dd211bfd2da26269f498
diff --git a/kokoro/ b/kokoro/
index a618501..3db3ea1 100644
--- a/kokoro/
+++ b/kokoro/
@@ -86,7 +86,5 @@
 for artifact in ${ARTIFACTS}
   cp ${artifact} ${KOKORO_ARTIFACTS_DIR}
+  chmod -x ${KOKORO_ARTIFACTS_DIR}/$(basename ${artifact})
-# Clear executable bit from artifacts