refactor(keepScanning): remove performance.now call

`requestAnimationFrame` handler already receives a timestamp as an
argument. No need to call `performance.now`.

Author: gruhn

src/misc/scanner.js

@@ -34,12 +34,10 @@ export function keepScanning (camera, options) {
   let locationBefore = null
   let lastScanned = performance.now()
 
-  const processFrame = () => {
+  const processFrame = timeNow => {
     if (shouldContinue()) {
       window.requestAnimationFrame(processFrame)
 
-      const timeNow = performance.now()
-
       if (timeNow - lastScanned >= minDelay) {
         lastScanned = timeNow