diff --git a/lib/json/index.js b/lib/json/index.js
index b13cf54..4229311 100644
--- a/lib/json/index.js
+++ b/lib/json/index.js
@@ -1,4 +1,6 @@
-var jsonFile = require('./jsonfile')
+'use strict'
+
+const jsonFile = require('./jsonfile')
 
 jsonFile.outputJsonSync = require('./output-json-sync')
 jsonFile.outputJson = require('./output-json')