Describe the bug
Sorting by namespace (shift-p) does not sort by namespace but by name.

To Reproduce
Steps to reproduce the behavior:

1. shift-p on pod view (or any other with namespace column)

Expected behavior
Should sort by namespace.

Screenshots
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Versions (please complete the following information):

• OS: Win7
• K9s 0.7.11
• K8s 1.13.7

Additional context
Add any other context about the problem here.