Set a name for k3d nightly

[LinuxSuRen]

Usage: ks install k3d --nightly latest

Result:

[root@node1 ~]# k3d cluster list
NAME               SERVERS   AGENTS   LOADBALANCER
nightly-20210926   1/1       1/1      true

[JohnNiang]

/lgtm

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@864ac6f). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master    #210   +/-   ##
========================================
  Coverage          ?   9.18%           
========================================
  Files             ?      32           
  Lines             ?    1394           
  Branches          ?       0           
========================================
  Hits              ?     128           
  Misses            ?    1256           
  Partials          ?      10           

Flag	Coverage Δ
unittests	9.18% <0.00%> (?)

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