Fix trailing whitespace after class

[Shinigami92]

close #439

[Shinigami92]

The example token stream is

[
{"type":"tag","loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":5}},"val":"html"},
{"type":"indent","loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":3}},"val":2},
{"type":"tag","loc":{"start":{"line":2,"column":3},"end":{"line":2,"column":7}},"val":"body"},
{"type":"indent","loc":{"start":{"line":3,"column":1},"end":{"line":3,"column":5}},"val":4},
{"type":"class","loc":{"start":{"line":3,"column":5},"end":{"line":3,"column":13}},"val":"wrapper"},
{"type":"text","loc":{"start":{"line":3,"column":13},"end":{"line":3,"column":14}},"val":" "},
{"type":"indent","loc":{"start":{"line":4,"column":1},"end":{"line":4,"column":7}},"val":6},
{"type":"class","loc":{"start":{"line":4,"column":7},"end":{"line":4,"column":17}},"val":"container"},
{"type":"text","loc":{"start":{"line":4,"column":18},"end":{"line":4,"column":25}},"val":"Content"},
{"type":"outdent","loc":{"start":{"line":5,"column":1},"end":{"line":5,"column":5}}},
{"type":"class","loc":{"start":{"line":5,"column":5},"end":{"line":5,"column":13}},"val":"wrapper"},
{"type":"text","loc":{"start":{"line":5,"column":14},"end":{"line":5,"column":15}},"val":" "},
{"type":"indent","loc":{"start":{"line":6,"column":1},"end":{"line":6,"column":7}},"val":6},
{"type":"class","loc":{"start":{"line":6,"column":7},"end":{"line":6,"column":17}},"val":"container"},
{"type":"text","loc":{"start":{"line":6,"column":18},"end":{"line":6,"column":25}},"val":"Content"},
{"type":"outdent","loc":{"start":{"line":7,"column":1},"end":{"line":7,"column":1}}},
{"type":"outdent","loc":{"start":{"line":7,"column":1},"end":{"line":7,"column":1}}},
{"type":"outdent","loc":{"start":{"line":7,"column":1},"end":{"line":7,"column":1}}},
{"type":"eos","loc":{"start":{"line":7,"column":1},"end":{"line":7,"column":1}}}
]

There are still trailing whitespaces after the classes, need to investigate later