Numeric tag causes python exception

[osresearch]

If a tag is a number it causes a type error:

ERROR   -  Exception in callback <bound method LiveReloadHandler.poll_tasks of <class 'livereload.handlers.LiveReloadHandler'>>
Traceback (most recent call last):
  File "/home/hudson/.local/lib/python3.7/site-packages/tornado/ioloop.py", line 907, in _run
    return self.callback()
  File "/home/hudson/.local/lib/python3.7/site-packages/livereload/handlers.py", line 69, in poll_tasks
    filepath, delay = cls.watcher.examine()
  File "/home/hudson/.local/lib/python3.7/site-packages/livereload/watcher.py", line 105, in examine
    func()
  File "/home/hudson/.local/lib/python3.7/site-packages/mkdocs/commands/serve.py", line 136, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "/home/hudson/.local/lib/python3.7/site-packages/mkdocs/commands/build.py", line 264, in build
    files = config['plugins'].run_event('files', files, config=config)
  File "/home/hudson/.local/lib/python3.7/site-packages/mkdocs/plugins.py", line 94, in run_event
    result = method(item, **kwargs)
  File "/home/hudson/.local/lib/python3.7/site-packages/tags/plugin.py", line 63, in on_files
    self.generate_tags_file()
  File "/home/hudson/.local/lib/python3.7/site-packages/tags/plugin.py", line 104, in generate_tags_file
    t = self.generate_tags_page(tag_dict)
  File "/home/hudson/.local/lib/python3.7/site-packages/tags/plugin.py", line 87, in generate_tags_page
    tags=sorted(data.items(), key=lambda t: t[0].lower()),
  File "/home/hudson/.local/lib/python3.7/site-packages/tags/plugin.py", line 87, in <lambda>
    tags=sorted(data.items(), key=lambda t: t[0].lower()),
AttributeError: 'int' object has no attribute 'lower'