TileLayer's number type offset cause blank map

[fuzhenn]

maptalks's version and what browser you use?

1.0.0-rc.6

Issue description

TileLayer's number type offset cause blank map

Please provide a reproduction URL (on any jsfiddle like site)

var map = new maptalks.Map('map', {
        center: [-0.113049, 51.503568],
        zoom: 14,
        // pitch : 56,
        // bearing : 30,
        centerCross: true,
        baseLayer: new maptalks.TileLayer('base', {
          offset: [10, 0],
          urlTemplate: 'https://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png',
          subdomains: ["a","b","c","d"],
          attribution: '&copy; <a href="http://osm.org">OpenStreetMap</a> contributors, &copy; <a href="https://carto.com/">CARTO</a>'
        })
      });

[deyihu]

https://codepen.io/deyihu/pen/QWQzPrr?editors=0010