only log stuff to the console if NODE_ENV=debug

fixes #275

lib/table.js

@@ -98,7 +98,7 @@ Table.prototype.addColumn = function(col, options) {
     } else {
       return this;
     }
-  } else if(!!this[col.name] && (process.env.NODE_ENV !== 'test')) {
+  } else if(!!this[col.name] && (process.env.NODE_ENV === 'debug')) {
     console.log('Please notice that you have just defined the column "' + col.name + '". In order to access it, you need to use "table.getColumn(\'' + col.name + '\');"!');
   }
   this.columns.push(col);