Add URL for viewing node coverage data on dev server.

Running test-js-with-node --coverage now provides a URL
to view the output data on the web.

Fixes #5177.

zerver/lib/test_helpers.py

@@ -396,6 +396,7 @@ def write_instrumentation_reports(full_suite):
             # static content URLs, since the content they point to may
             # or may not exist.
             'coverage/(?P<path>.*)',
+            'node-coverage/(?P<path>.*)',
             'docs/(?P<path>.*)',
         ])