Add `sync` command to shell completion scripts

Fixes #1549

etc/hub.bash_completion.sh

@@ -22,6 +22,7 @@ create
 browse
 compare
 ci-status
+sync
 EOF
     __git_list_all_commands_without_hub
   }

etc/hub.fish_completion

@@ -24,6 +24,7 @@ complete -f -c hub -n '__fish_hub_needs_command' -a create -d "create new repo o
 complete -f -c hub -n '__fish_hub_needs_command' -a fork -d "fork origin repo on GitHub"
 complete -f -c hub -n '__fish_hub_needs_command' -a pull-request -d "open a pull request on GitHub"
 complete -f -c hub -n '__fish_hub_needs_command' -a ci-status -d "display GitHub Status information for a commit"
+complete -f -c hub -n '__fish_hub_needs_command' -a sync -d "update local branches from upstream"
 
 # alias
 complete -f -c hub -n ' __fish_hub_using_command alias' -a 'bash zsh sh ksh csh fish' -d "output shell script suitable for eval"

etc/hub.zsh_completion

@@ -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
   }