message: use key in <link> map() output
diff: @@ -20,8 +20,8 @@ const Meta = () => (
  <React.Fragment>
  <meta name='viewport' content='width=device-width,initial-scale=1' />
  <meta name='generator' content='Compositor X0' />
  - {primerPackages.map(pkg => (
  - <link rel='stylesheet' href={`https://unpkg.com/${pkg}/build/build.css`} />
  + {primerPackages.map((pkg, key) => (
  + <link rel='stylesheet' href={`https://unpkg.com/${pkg}/build/build.css`} key={key} />
  ))}
  <link rel='icon' href='assets/favicon.png' />
  <link rel='apple-touch-icon' href='assets/apple-touch-icon.png' />
  