ESLint fixes

src/core/components/version-stamp.jsx

@@ -1,5 +1,12 @@
 import React from "react"
+import PropTypes from "prop-types"
 
-export default ({ version }) => {
+const VersionStamp = ({ version }) => {
   return <small><pre className="version"> { version } </pre></small>
 }
+
+VersionStamp.propTypes = {
+  version: PropTypes.string.isRequired
+}
+
+export default VersionStamp