message: Use `declare module.exports` syntax for flow libdefs
  We added this to Flow in v0.25 (about 2 years ago), but never actually
  deprecated the legacy `declare var exports` syntax. Hoping to do that
  soon, so clearing up uses that I can find.
  Test Plan: flow
diff: @@ -17,8 +17,8 @@ declare module "resolve/lib/node-modules-paths" {
  moduleDirectory: Array<string>,
  };
  - declare function exports(
  + declare module.exports: (
  path: string,
  options: NodeModulesPathsOptions,
  - ): Array<string>;
  + ) => Array<string>;
  }
  