fix(ssh-add): option parsing with recent versions

At least 9.3p1 outputs usage style, and we're already using the usage ->
help fallback pattern for ssh-keygen.

Author: scop

completions/ssh-add

@@ -37,7 +37,7 @@ _comp_cmd_ssh_add()
     esac
 
     if [[ $cur == -* ]]; then
-        _comp_compgen_help -- '-?'
+        _comp_compgen_usage -- '-?' || _comp_compgen_help -- '-?'
         return
     fi