fix typo

Author: zloirock

packages/core-js/modules/es.symbol.description.js

@@ -31,15 +31,15 @@ if (DESCRIPTORS && typeof NativeSymbol == 'function' && (!('description' in Nati
   symbolPrototype.constructor = SymbolWrapper;
 
   var symbolToString = symbolPrototype.toString;
-  var nativeString = String(NativeSymbol('test')) == 'Symbol(test)';
+  var nativeSymbol = String(NativeSymbol('test')) == 'Symbol(test)';
   var regexp = /^Symbol\((.*)\)[^)]+$/;
   defineProperty(symbolPrototype, 'description', {
     configurable: true,
     get: function description() {
       var symbol = isObject(this) ? this.valueOf() : this;
       var string = symbolToString.call(symbol);
       if (has(EmptyStringDescriptionStore, symbol)) return '';
-      var desc = nativeString ? string.slice(7, -1) : string.replace(regexp, '$1');
+      var desc = nativeSymbol ? string.slice(7, -1) : string.replace(regexp, '$1');
       return desc === '' ? undefined : desc;
     }
   });