Added node pre-build steps to run_tests.py

tools/run_tests/run_tests.py

@@ -191,7 +191,8 @@ class NodeLanguage(object):
                             environ=_FORCE_ENVIRON_FOR_WRAPPERS)]
 
   def pre_build_steps(self):
-    return []
+    # Default to 1 week cache expiration
+    return [['npm', 'update', '--cache-min', '604800']]
 
   def make_targets(self):
     return []