fix setPosition 在元素没有设置margin－left时无法正确计算的bug。see https://github.com/BaiduFE/Tangram-base/issues#issue/45
fix setPosition 在元素没有设置margin－left时无法正确计算的bug。see https://github.com/BaiduFE/Tangram-base/issues#issue/45

cnberg/Tangram-base,BaiduFE/Tangram-base,BaiduFE/Tangram-base,cnberg/Tangram-base,cnberg/Tangram-base,BaiduFE/Tangram-base