K9s: Pulse view - cpu and memory options errors out.

[azarudeena]

Describe the bug
In k9s Pulse view, the CPU and Memory selections are returning error screen.

To Reproduce
Steps to reproduce the behavior:

1. Go to Pulse view
2. tab to cpu or memory
3. click enter
4. See error

Expected behavior
Not sure. Either sorted list of pods based on the selection of Pods or CPUs.

Versions (please complete the following information):

• OS: Ubuntu 18
• K9s 0.20.5
• K8s 1.18

Additional context
Add any other context about the problem here.

[derailed]

@azarudeena - Should be happier in v0.21.0...

[azarudeena]

Awesome!!! Working great.