fix underscore method for single letter words

Author: az7arul

lib/string.js

@@ -558,7 +558,7 @@ string.js - Copyright (C) 2012-2014, JP Richardson <[email protected]>
 
     //#modified from https://github.com/epeli/underscore.string
     underscore: function() {
-      var s = this.trim().s.replace(/([a-z\d])([A-Z]+)/g, '$1_$2').replace(/[-\s]+/g, '_').toLowerCase();
+      var s = this.trim().s.replace(/([a-z\d])([A-Z]+)/g, '$1_$2').replace(/([A-Z\d]+)([A-Z][a-z])/,'$1_$2').replace(/[-\s]+/g, '_').toLowerCase();
       return new this.constructor(s);
     },
 

test/string.test.js

@@ -680,6 +680,7 @@
         F (S('CarSpeed').underscore().s === '_car_speed');
         T (S('_CarSpeed').underscore().s === '_car_speed');
         T (S('yesWeCan').underscore().s === 'yes_we_can');
+        T (S('oneAtATime').underscore().s === 'one_at_a_time');
       })
     })