hyper-parameter not shown correctly in WebUI when there is only one hyper parameter

[suiguoxin]

<Short summary about the issue/question:
hyper-parameter not shown correctly in WebUI when there is only one parameter

Brief what process you are following:
Run experiment where there is only one hyper parameter defined in search space.

How to reproduce it:

nni Environment:

• nni version: 0.8
• nni mode(local|pai|remote): local
• OS:
• python version: 3
• is conda or virtualenv used?: conda
• is running in docker?: no

need to update document(yes/no): no

Anything else we need to know: