[fix] Lazy-load any CLI arguments from `optimist`

lib/nconf/provider.js

@@ -6,7 +6,6 @@
  */
 
 var async = require('async'),
-    optimist = require('optimist'),
     common = require('./common'),
     stores = require('./stores');
 
@@ -236,7 +235,11 @@ Provider.prototype.__defineGetter__('useArgv', function () {
 //
 Provider.prototype.__defineSetter__('useArgv', function (val) {
   this._useArgv  = val            || false;
-  this.overrides = this.overrides || optimist.argv;
+  
+  if (this._useArgv) {
+    this._argv     = this._argv     || require('optimist').argv;
+    this.overrides = this.overrides || this._argv;
+  }
 });
 
 //