Simplify hub check and hardcode aliasing (#6767)

* Simplify hub check and hardcode aliasing

* Update hub completion

plugins/github/_hub

@@ -89,6 +89,7 @@ __hub_setup_zsh_fns () {
       browse:'browse the project on GitHub'
       compare:'open GitHub compare view'
       ci-status:'lookup commit in GitHub Status API'
+      sync:'update local branches from upstream'
     )
     _describe -t hub-commands 'hub command' hub_commands && ret=0
 
@@ -115,6 +116,7 @@ create
 browse
 compare
 ci-status
+sync
 EOF
     __git_list_all_commands_without_hub
   }

plugins/github/github.plugin.zsh

 # Set up hub wrapper for git, if it is available; http://github.com/github/hub
-if [ "$commands[(I)hub]" ]; then
-  if hub --version &>/dev/null; then
-    eval $(hub alias -s zsh)
-  fi
+if (( $+commands[hub] )); then
+  alias git=hub
 fi
 
 # Functions #################################################################