Rename exportOnlyLocals to onlyLocals in css-loader option

[tychenjiajun]

Summary

webpack/css-loader#957

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• Bugfix
• Feature
• Code style update
• Refactor
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• No

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Other information:

[ulivz]

Thanks, but this change was introduced in css-loader@3, while VuePress depends on css-loader@2.

[tychenjiajun]

@ulivz We have a problem migrating from 0.14.11 to 1.0.x. When using 0.x versions, we can build successfully. But we have the following error in building process after switching the version.

ModuleBuildError: Module build failed (from ./node_modules/css-loader/dist/cjs.js):
ValidationError: Invalid options object. CSS Loader has been initialised using an options object that does not match the API schema.
 - options has an unknown property 'exportOnlyLocals'. These properties are valid:
   object { url?, import?, modules?, sourceMap?, importLoaders?, localsConvention?, onlyLocals? }

Our own project depends on css-loader@3 and it seems like the problem here is caused by the different versions our project and vuepress depend on. Is there any proper way to override the css-loader option?