Update dependency vue-loader to v15.9.7

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
vue-loader	15.9.6 -> 15.9.7

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Release Notes

vuejs/vue-loader

### [`v15.9.7`](https://togithub.com/vuejs/vue-loader/blob/master/CHANGELOG.md#​1597-httpsgithubcomvuejsvue-loadercomparev1596v1597-2021-05-11) [Compare Source](https://togithub.com/vuejs/vue-loader/compare/v15.9.6...v15.9.7) ##### Bug Fixes - [plugin] Use compiler.webpack when possible ([#​1822](https://togithub.com/vuejs/vue-loader/issues/1822)) ([f7ee30b](https://togithub.com/vuejs/vue-loader/commit/f7ee30b)), closes [#​1781](https://togithub.com/vuejs/vue-loader/issues/1781) - check for compiler.webpack existence ([2472b2f](https://togithub.com/vuejs/vue-loader/commit/2472b2f))

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Configuration

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