Fix validation errors in plugin documentation (#399) (#458)

[backport/2.2] Fix validation errors in plugin documentation (#399)

Fix validation errors in plugin documentation
SUMMARY
This fixes validation errors in plugin documentation now that ansible
test for 2.13 is running validate-modules on all plugins. The kubectl
connection plugin validation is ignored because there seems to be a
requirement for the author field to have a github username, which we do
not have.
ISSUE TYPE
Docs Pull Request
COMPONENT NAME
plugins/connection/kubectl
plugins/inventory/k8s
plugins/lookup/k8s
plugins/lookup/kustomize
ADDITIONAL INFORMATION
Reviewed-by: None 
(cherry picked from commit 30e84fa)

plugins/inventory/k8s.py

@@ -6,10 +6,9 @@ __metaclass__ = type
 
 DOCUMENTATION = '''
     name: k8s
-    plugin_type: inventory
     author:
-      - Chris Houseknecht <@chouseknecht>
-      - Fabian von Feilitzsch <@fabianvf>
+      - Chris Houseknecht (@chouseknecht)
+      - Fabian von Feilitzsch (@fabianvf)
 
     short_description: Kubernetes (K8s) inventory source