fix: iOS9以下svg引起的Modal展示问题

[ziluo]

业务线反馈在iOS 9.2的真机上Modal无法正常展示，初步排查后发现是由于同时使用了Icon组件，经过详细定位后发现是引入Svg的时机问题，如果Svg延后引入就没问题，和

ant-design-mobile/components/icon/loadSprite.tsx

Line 3 in caeff3d

// Much simplified, do make sure run this after document ready

描述的问题有点类似，经测试发现把Svg的样式position: absolute删除即可解决问题，实测在iOS8、iOS9以及最新的iOS版本均可正常展示

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This change is 

[paranoidjk]

出处应该是 https://github.com/JetBrains/svg-mixer/blob/master/packages/svg-mixer/runtime/src/sprite.config.js#L9

兼容性问题没啥好 review 的，这里本意只是想渲染但是不展示，表现不一致就得靠测了

[codecov]

Codecov Report

Merging #3229 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3229   +/-   ##
=======================================
  Coverage   60.07%   60.07%           
=======================================
  Files          92       92           
  Lines        2282     2282           
  Branches      656      656           
=======================================
  Hits         1371     1371           
  Misses        902      902           
  Partials        9        9

Flag	Coverage Δ
#web	60.07% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
components/icon/loadSprite.tsx	26.66% <ø> (ø)	⬆️
components/locale-provider/locale-provider.tsx	100% <0%> (ø)	⬆️

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