fix(ri): work around localvar_inherit

Author: akinomyoga

completions/ri

@@ -66,7 +66,7 @@ _comp_cmd_ri()
         return
     fi
 
-    local class method prefix ri_path ri_version ri_major separator IFS
+    local class method prefix="" ri_path ri_version ri_major="" separator IFS
     local -a classes
 
     ri_path=$(type -p ri)