diff --git a/src/shell/environment.js b/src/shell/environment.js
index a86a625..8c0c52b 100644
--- a/src/shell/environment.js
+++ b/src/shell/environment.js
@@ -1,4 +1,5 @@
-var defaults = require('../constants.js').ENVIRONMENT;
+'use strict'; 
+const defaults = require('../constants.js').ENVIRONMENT;
 
 module.exports = function Environment(env) {
   env = env || {};