upgrade loader-utils to handle `cloud://...` url

[imyelo]

云开发存储的文件可以在 wxml 里用的组件以 cloud://... 为地址使用：

https://developers.weixin.qq.com/miniprogram/dev/wxcloud/guide/storage.html

例如：

<image src="cloud://foo.bar/fixture.gif" />

[coveralls]

Pull Request Test Coverage Report for Build 50

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.517%

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Totals
Change from base Build 49:	0.0%
Covered Lines:	87
Relevant Lines:	90

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💛 - Coveralls