Update web-vitals calls

The `getXXX()` functions of the `web-vitals` library were renamed in
3.0.0 to `onXXX()` [1]. Fix our calls to reflect this.

[1]: GoogleChrome/web-vitals#222

src/reportWebVitals.ts

@@ -2,12 +2,12 @@ import { ReportHandler } from 'web-vitals';
 
 export const reportWebVitals = (onPerfEntry?: ReportHandler) => {
   if (onPerfEntry && onPerfEntry instanceof Function) {
-    import('web-vitals').then(({ getCLS, getFID, getFCP, getLCP, getTTFB }) => {
-      getCLS(onPerfEntry);
-      getFID(onPerfEntry);
-      getFCP(onPerfEntry);
-      getLCP(onPerfEntry);
-      getTTFB(onPerfEntry);
+    import('web-vitals').then(({ onCLS, onFID, onFCP, onLCP, onTTFB }) => {
+      onCLS(onPerfEntry);
+      onFID(onPerfEntry);
+      onFCP(onPerfEntry);
+      onLCP(onPerfEntry);
+      onTTFB(onPerfEntry);
     });
   }
 };