fix(git): Fix zsh completion for aws plugin.

This is following the documentation for completion from aws here
https://docs.aws.amazon.com/cli/v1/userguide/cli-configure-completion.html. I
imagine this may work if other plugins are executed before this that perform
this action already, but it was broken for me.

plugins/aws/aws.plugin.zsh

@@ -296,6 +296,7 @@ fi
 # AWS CLI v2 comes with its own autocompletion. Check if that is there, otherwise fall back
 if command -v aws_completer &> /dev/null; then
   autoload -Uz bashcompinit && bashcompinit
+  autoload -Uz compinit && compinit
   complete -C aws_completer aws
 else
   function _awscli-homebrew-installed() {