Update _Form.styl

[nakoshi-k]

Description

fix issue#4

• Bypass the stylus built-in uri function.

Code sample

_url(path)
  s( "url('" + path + "')")

  background: _url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 30 8" width="30"><path fill="' + color-quaternary + '" d="M0,0l6,8l6-8"/></svg>',"utf8") center right no-repeat
  padding-right: 3.0rem