Declared Bui agents don't show in Burp-UI

Hello,

When setting up bui-agents, if the agent name in burpui.cfg contains a dash, no agent will show, without any further error message.

Example of failing configuration in /etc/burp/burpui.cfg [Agent:agent-1]

Working configuration is [Agent:agent1]

As this is a trivial bug, a quick comment about this in burpui.cfg would be a little time saver.

Burp versio: 2.1.16 Burp-UI version: v0.5.1 (stable) Python version: 2.7.5

Best regards.