add CatchClause scope

lib/6to5/traverse/scope.js

@@ -37,6 +37,8 @@ Scope.prototype.getIds = function () {
         return false;
       }
     });
+  } else if (t.isCatchClause(block)) {
+    self.add(block.param, ids);
   }
 
   if (t.isFunction(block)) {

lib/6to5/types/alias-keys.json

@@ -23,6 +23,7 @@
 
   "BlockStatement": ["Statement", "Scope"],
   "Program":        ["Scope"],
+  "CatchClause":    ["Scope"],
 
   "LogicalExpression": ["Binary"],
   "BinaryExpression":  ["Binary"],