Replace thier with their

lib/module.js

@@ -49,7 +49,7 @@ function Module(id, parent) {
 module.exports = Module;
 
 // Set the environ variable NODE_MODULE_CONTEXTS=1 to make node load all
-// modules in thier own context.
+// modules in their own context.
 Module._contextLoad = (+process.env['NODE_MODULE_CONTEXTS'] > 0);
 Module._cache = {};
 Module._pathCache = {};