Tell eslint to allow usage of dev dependencies in frontend code.

src/.eslintrc.yaml

@@ -0,0 +1,4 @@
+rules:
+  import/no-extraneous-dependencies:
+    - error
+    - devDependencies: true

src/Countdown.jsx

@@ -9,9 +9,6 @@ import style from './Countdown.sass';
 export default class Countdown extends React.Component {
   static propTypes = {
     date: PropTypes.instanceOf(moment).isRequired,
-    locale: PropTypes.string,
-    minimumIntegerDigits: PropTypes.number,
-    useGrouping: PropTypes.bool,
     getNow: PropTypes.func,
   };
 
@@ -57,7 +54,6 @@ export default class Countdown extends React.Component {
 
     const size = 160; // @HACK
 
-    const { locale, minimumIntegerDigits, useGrouping } = this.props;
     return (
       <div className={style.countdown}>
         <ProgressCircle size={size} max={3} progress={days} stroke="rgb(76,114,163)">