Yarn v1.10 adds `integrity`s but v1.9 removes them. Add this option to prevent them from adding unnecessary diffs all the time. This is the default value for Yarn v1.12+ (ref: yarnpkg/yarn#6465).
Now, `yarn add` and `yarn upgrade` will write exact versions to package.json and yarn.lock. See commit fadbbeb (https://github.com/prettier/prettier/pull/291)
fadbbeb