in es3, "use strict" should not be parsed as directive

no nodes should be parsed as [Directive](https://github.com/estree/estree/blob/master/es5.md#directive) nodes in ES3 mode. it was found in https://github.com/eslint/espree/pull/547#discussion_r858617318

related: https://github.com/acornjs/acorn/commit/353e24f72bd4b8d4cba3755498bdc862540b4659