[angular-formly] formlyConfig.setWrapper - accept array of wrapper configs

[zuzusik]

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If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes: http://docs.angular-formly.com/docs/formlyconfig#setwrapper (look at Example section, after array API comment)

[dt-bot]

types/angular-formly/index.d.ts

to author (@scatcher). Could you review this PR?
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• pass the Travis CI test?

[typescript-bot]

This PR has been open and unchanged 5 days without signoff or complaint. This will be merged by a maintainer soon if there are no objections.