Handle log-level as case-insensitive

JupyterHub passes `debug` when `c.ConfigurableHTTPProxy.debug=True`

Author: manics

configurable_http_proxy/cli.py

@@ -126,7 +126,8 @@ def convert(self, value, param, ctx):
 @click.option(
     "--log-level",
     type=click.Choice(
-        [logging.getLevelName(i) for i in (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR)]
+        [logging.getLevelName(i) for i in (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR)],
+        case_sensitive=False,
     ),
     help='Log level (debug, info, warning, error) (default: "info")',
 )