fix linting errors

src/components/generics/useInterval.js

@@ -3,7 +3,6 @@ import { useRef, useEffect } from 'react'
 // from: https://overreacted.io/making-setinterval-declarative-with-react-hooks/
 export function useInterval(callback, delay) {
   const savedCallback = useRef()
-  const x = 'asdf'
   // Remember the latest callback.
   useEffect(() => {
     savedCallback.current = callback

src/lib/array-util.js

@@ -25,6 +25,6 @@ export function getNextSmallerNumber(num, sortedArray) {
   return null
 }
 
-function lastEntry(arr) {
+export function lastEntry(arr) {
   return arr[arr.length - 1]
 }