use string key for keywords for older browser compatibility

src/api/global.js

@@ -36,7 +36,7 @@ exports.extend = function (extendOptions) {
     Super.options,
     extendOptions || {}
   )
-  Sub.super = Super
+  Sub['super'] = Super
   // allow further extension
   Sub.extend = Super.extend
   // create asset registers, so extended classes

src/compile/compile.js

@@ -324,7 +324,7 @@ function compileParamAttributes (el, attrs, options) {
  */
 
 function makeParamsLinkFn (params, options) {
-  var def = options.directives.with
+  var def = options.directives['with']
   return function paramsLinkFn (vm, el) {
     var i = params.length
     var param