Revert "kubectl: rename k alias" (#7817)

This reverts commit 978b724c (#7749)

See https://github.com/robbyrussell/oh-my-zsh/issues/6408#issuecomment-485718042 and later comments.

plugins/kubectl/README.md

@@ -13,7 +13,7 @@ plugins=(... kubectl)
 
 | Alias   | Command                             | Description                                                                                      |
 |:--------|:------------------------------------|:-------------------------------------------------------------------------------------------------|
-| ku      | `kubectl`                           | The kubectl command                                                                              |
+| k       | `kubectl`                           | The kubectl command                                                                              |
 | kca     | `kubectl --all-namespaces`          | The kubectl command targeting all namespaces                                                     |
 | kaf     | `kubectl apply -f`                  | Apply a YML file                                                                                 |
 | keti    | `kubectl exec -ti`                  | Drop into an interactive terminal on a container                                                 |

plugins/kubectl/kubectl.plugin.zsh

@@ -10,7 +10,8 @@ if (( $+commands[kubectl] )); then
     unset __KUBECTL_COMPLETION_FILE
 fi
 
-alias ku=kubectl
+# This command is used a LOT both below and in daily life
+alias k=kubectl
 
 # Execute a kubectl command against all namespaces
 alias kca='f(){ kubectl "$@" --all-namespaces;  unset -f f; }; f'